CHAPTER 3 PROJECT DESCRIPTION AND SITE CONDITION

Transcription

1 19 CHAPTER 3 PROJECT DESCRIPTION AND SITE CONDITION 3.1 OVERVIEW This chapter describes Route 44 relocation project. General project information is provided along with details related to the subsurface conditions at the site, the characteristics and engineering parameters of the peat and backfill soils, the design and construction of the embankments, excavations, fills, and retaining walls. Section 3.3 provides the original site information prepared by the Massachusetts Highway Department (MHD) and developed by Ernst et al. (1996). Section 3.5 presents the characteristics and engineering parameters of Carver peat and is based on the research presented in our first report by Paikowsky and Elsayed (23). 3.2 ROUTE 44 RELOCATION PROJECT Section I of Route 44 project starts in the town of Carver in the vicinity of Route 58 and extends approximately 6.3 miles eastward to meet Section II in Kingston near the Plymouth and Kingston town line. The proposed highway is a four lane divided highway with a typical median width of 6 feet. The project includes the construction of eight on/off ramps and reconstruction or realignment of portions of four secondary roadways that intersect the proposed highway. Preliminary plans show that cut sections of up to 4 feet and embankment fills of up to 35 feet are required. To minimize the embankments fill impact on the wetland, eight retaining walls with a cumulative length of approximately 1.5 miles and twelve steepened 1:1 embankments slopes with a cumulatively length of approximately.5 miles are required. Many of the walls pass through cranberry bogs and wetland areas underlain by organic soils that are up to 35 feet thick. The walls that pass through cranberry bogs are flanked by an access road 25 feet wide just above the elevation of the bog. Figure 3.1 presents a completed section of the embankment, MSE wall, access road and capped sheet pile. The picture was taken in April 25 prior to the roadway completion. 3.3 ORIGINAL SITE INFORMATION Subsurface Investigation and Field Testing The original site information is provided in the Massachusetts Highway Department (MHD) geotechnical report entitled Geotechnical Report for Relocated Route 44, Section I Carver, Plympton and Kingston authored by Ernst et al. (1996). Excerpts of the report are provided in Appendix A. The preliminary subsurface investigation for Section I was performed in January and February of 1988 by Guild Drilling Company under a contract with the Massachusetts Highway Department (MHD). A total of 21 drive sample borings and 216 probe soundings into organics were taken along the proposed location of the highway walls and bridges. Figure 3.2 presents the geologic profile of Route 44 section I. It can be observed that peat layers are mainly located around stations 11+, 117+5, 141+, 143+5, 156+ and Figures 3.3 to 3.6 contain the boring logs and probe results for these

2 11 investigations. These borings and probes were taken as a portion of the pilot boring program for the entire Route 44 relocation project performed by Pavlo Engineering Company. Further subsurface information was obtained from a boring program performed from July 1995 to February Borings, test pits and additional peat probes were taken by Carr Dee Corporation, of Medford Massachusetts, under contract with the MHD. The boring program involved a total of 253 drive sample borings, 22 test pits and 22 additional peat probes at various locations along the proposed route to obtain specific subsurface information. Of the 253 borings, 45 were drilled at proposed bridge locations and 56 additional borings were drilled at proposed wall location. To obtain ground water level information for design of the highway structures, observation wells were installed in 2 of the completed borings. The locations of these borings, wells and test pits around the five instrumented stations are shown on the boring plan of figure 3.7. All borings were drilled using rotary bits and water jetting to advance the hole, and steel casing was used to maintain borehole stability. The borings taken for the proposed highway were drilled to predetermined highest bottom elevations and extended at least 1 feet into suitable granular material and at least 1 feet below the proposed grade. Wall borings were drilled until bedrock or refusal (12 blows per 12 penetration) was encountered, or to a depth considered adequate by the geotechnical engineer for the design of shallow foundation in medium dense sand. Cores ten feet into bedrock were obtained in 34 out of 253 borings taken. Eight of the observation wells were installed in the borings for the design of recharge basins. The installed observation wells each have a 15 feet screen length, approximately 1 feet of which is below the existing groundwater table. During the drilling of the boreholes, falling head permeability/infiltration tests were conducted below the invert elevations of the proposed recharge basins by MHD personnel. CPTU and SCPTU Testing were performed by Write Padgett Christopher (WPC) with the plane view of the test locations presented in Appendix B. MHD personnel were responsible for the layout, field survey, and inspection of each boring. Classification of soil and rock samples was performed visually in the field by the driller. These samples were later reviewed at MHD Research and Material Lab in south Boston and found to be consistent with drillers classification Laboratory Testing To investigate the engineering properties of the peat found along the proposed route, extensive laboratory study was carried out at the University of Massachusetts Lowell and is described by Paikowsky and Elsayed (23). Several undisturbed tube (square 1 inch 1inch ) samples of the peat were obtained from the bog surface downward. Before driving the tube for sampling into the bog, four triangular stiff plastic segments were attached at the lower tip of the tube to serve as retainers and are shown in Figure 3.8. The retainers were aimed to prevent the sample from coming out when the tube was pulled out of the bog. Figure 3.9 shows the procedure used for driving the square samplers into the peat. The obtained peat samples are shown in figure 3.1. Since the organic soils were found in areas where fill is proposed, a consolidation test with a long term (1, hour) load increment at 2.6 ksf was performed to help predict settlements for the case that some of the organics are left in place. The information obtained

3 111 from section II consists of three consolidation tests and two triaxial strength tests (CIU type). Several index tests of water content, organic content, unit weight and PH were performed as well, (see Appendix A). Twelve consolidation tests and fourteen Triaxial tests were performed at the Geotechnical Engineering Research Laboratory at UMASS Lowell (Paikowsky and Elsayed, 23). The test results and related engineering properties of the peat at Route 44 are introduced in section 3.4. A series of lab tests including direct shear test, triaxial tests and field tests including CPT and SPT tests on the backfill were also performed to study engineering properties of the sand and are introduced in section SUBSURFACE CONDITION AND CONSTRUCTION RECOMMENDATION Throughout the project location, the surficial geology is shown as stratified beds and lenses of well sorted fine to coarse sand with some lenses of gravel, silt and clay. Within 5 feet of the Winnetuxet river, the soils are shown however as stratified beds and lenses of fine sand, silt and clay, with few lenses of gravel and medium to coarse sand. Based on the boring logs and peat probes, soil profiles were drawn along each of the proposed walls. The profiles show that the general soil type and density is relatively consistent throughout the project. A thin veneer of topsoil overlies deep deposits of coarse to fine sand with some gravel or silt and occasional cobbles and boulders. The organic soils immediately below the surface in the cranberry bog and wetland areas consist primarily of fiberous peat, whereas the organic deposits beneath the pond around station 141+ to station 16+ (see figure 3.2) consist primarily of muck and amorphous peat. Since the organic deposits present the major obstacles to the construction of the highway, it was determined to excavate all the organic deposits at the embankments location and replace with granular backfill using a sheet pile wall as a retaining structure. Detailed information about the site conditions and construction in organic deposits are provided in the MHD geotechnical report presented in Appendix A. 3.5 PEAT CHARACTERISTICS AND ENGINEERING PARAMETERS Peat is an organic residue formed through the decomposition of plant and animal body under the aerobic and anaerobic conditions associated with low temperatures and geological effects such as glacial ice. Common names for accumulation of organic soils include bog, fen, moor, muck, and muskeg. Cranberry bogs at Carver Massachusetts are the result of organic deposit accumulation over a lengthy period of time in kettle holes created by glaciers. Carver peat exhibits poor bearing capacity, high compressibility, and long-term deformation under constant loading (creep effect). A series of laboratory tests including permeability, consolidation, triaxial and direct shear tests had been performed on horizontal and vertical samples at the University of Massachusetts, Lowell (Paikowsky and Elsayed, 23). Table 3.1 summarizes the index properties and engineering parameters of Carver peat.

4 CHARACTERISTICS AND ENGINEERING PARAMETERS OF THE BACKFILL MATERIAL Overview Parts of the new highway alignment (Route 44) span across existing cranberry bogs. At these roadway sections, sheet piling has been placed and the cranberry bogs have been excavated between the sheet piling. After the excavation of the organic material within the bogs (peat), these sections were backfilled with granular material. Since the site was not dewatered during the backfilling operations, it was suspected that these sands would be in a loose, saturated state, making them susceptible to liquefaction. Deep Dynamic Compaction (DDC) and Vibrofloatation-Compaction (VC) were therefore planned for these areas to support the Mechanically Stabilized Earth (MSE) walls to be constructed on the top of the compacted soils carrying the raised highway. To verify the effectiveness of the deep dynamic compaction, Cone Penetration Testing (CPT) was performed before and after the compaction. The engineering parameters of the backfill material were determined for use in the FEM analysis of the soil-wall interaction. A series of laboratory tests were conducted and cone penetration tests were interpreted in order to determine the engineering parameters of the backfill materials. Triaxial and direct shear tests were employed to test the strength parameters of the backfill material. PCPT data were also available to explore the soil profiles at the five instrumented stations, to assess the liquefaction properties and to verify the effectiveness of the DDC test to improve the strength of the backfill Laboratory Tests Analysis Sieve Analysis A backfill material sample for the laboratory tests was obtained from a two feet test pit below surface at station (L). A sieve analysis test was performed and the grain size distribution is presented in figure From figure 3.11, it can be seen that the fill material consists mainly of sands with some trace of silt, clay and gravels. Based on the liquefaction assessment standard provided by Tsuchida (197), it can be seen that the backfill material is susceptible to liquefaction by earthquake shaking or other rapid loading. The liquefaction properties are further examined using the PCPT test results Triaxial Test Results Three triaxial tests were carried out on samples obtained from different depth using confining pressures, σ c, of 4.2 psi, 8.3 psi and 12.5 psi without back pressure. The tested samples unit weights were 125pcf, 126pcf and pcf as summarized in table 3.2. Figure 3.12 presents the stress-strain relations for the triaxial tests. It can be seen that the maximum deviatoric stress appears before the axial strain is about 7%. The maximum deviatoric stress increases with the increasing of confining pressure. Under the higher confining stresses, the material exhibits a strain-softening behavior. Figure 3.13 presents the Mohr-Column failure

5 113 envelope of the backfill material samples for peak shear conditions (a) and residual state (b). The friction angle is about 38.9 for the peak strength and 29. for the residual state. Based on the stress-strain relationship, the initial elastic modulus E i and secant elastic modulus E 5 are obtained, where E i is the slope of the stress-strain curve before axial strain is 4%, and E 5 is the slope of the stress-strain curve at 5% of peak stress. The failure elastic modulus E failure is calculated from the stress-strain curve at the peak stress. Table 3.2 summarizes the triaxial test results of the fill Direct Shear Tests A series of direct shear tests were performed in order to determine the shear strength of the fill and the results are summarized in table 3.3. Figure 3.14 presents the stress-strain curves obtained in the tests. It can be seen that before reaching the peak failure, the shear stress increases with the shear displacement. After undergoing the peak failure, the dense sands soften with the shear strain until the stable state. Figure 3.15 presents the fills peak failure friction angle φ p and residual friction angle φ R values. The peak failure friction angle is in good agreement with that from the triaxial tests. The residual friction angle is larger than the value obtained from the triaxial tests Cone Penetration Test (CPT) Overview The Cone Penetration Test (CPT) is an important tool in the exploration of cohesionless soils as laboratory testing is generally not feasible due to the difficulty of obtaining undisturbed samples. CPT is useful in profiling, identification, and assessing engineering parameters including angle of shearing resistance and deformation characteristics of cohesionless soils. A CPT device consists of a cylindrical probe with a cone-shaped tip with different sensors that allow real time continuous measurements of tip and frictional resistance to penetration while the cone is pushed into the ground at a speed of 2 cm/s. The typical CPT probe measures the stress on the tip, the sleeve friction and the pore water pressure. Some cones are equipped with a geophone in order to be able to perform shear wave velocity measurements. The data is normally read by a field computer that displays real-time data and stores it at regular depth intervals. Measurements can be taken at any intervals desired. Figure 3.16 depicts a typical cone penetration test. There are several configurations of cones that vary mainly in the position of the pore pressure element. These different configurations are presented in figure The piezocone can measure the pore pressure by advancing the cone with a pore pressure probe into the subsurface. Following the fill placement, the Piezocone Penetration Test (PCPT) was used to verify the quality and completeness of the backfill material and its strength before and after the compaction. These tests were conducted and performed by Wright Padgett Christopher (WPC) of South Carolina in accordance with ASTM D5778 Standard Test Method for Performing Electronic Friction Cone and Piezocone Penetration testing of soils. The tests locations are provided in Appendix B. The PCPT data of the backfill near the five

6 114 instrumented stations of Route 44 at Carver MA were analyzed in order to obtain the backfill profiling and engineering parameters to be used in the FEM analysis of the soil-wall interaction. Additional analyses examining the CPT and Seismic Cone Penetration Testing (SCPT) at the site are presented by Hajduk et al. (24) Profiling and Soil Identification Soil identification can be achieved from the magnitude of the cone resistance, and more specifically from the friction ratio (i.e. the ratio of local side friction to cone resistance) at the same level. A scheme of identification using the Dutch mechanical friction sleeve tip was first formulated by Begemann (1965) and extended by Schmertmann (1969). A comprehensive scheme was formulated by Douglas and Olsen (1981). A simplified working version was formulated by Robertson and Campanella (1983). The profiling and soils identification for the backfill at the five instrumented stations are based on the simplified working version suggested by Robertson and Campanella. (1) Station 11+ Figure 3.18 presents the PCPT results for the backfill at station 11+. Profiling was determined based on Robertson and Campanella (1983). Figure 3.19 shows the soil identification considering the relation of cone resistance and friction ratio. For the backfill at station 11+, the soil mainly consists of sands with thin layers of silty sand and clayey silt located at the upper layers. The initial water table level in the backfill was at a depth of about 11 feet from the surface. Because DDC was planned to be employed, it is important to determine whether the soils can be improved by deep compaction. Mitchell (1982) identified soils according to grain size distribution and suggested that most granular soils with a fine content (particles sizes<.64 mm) lower than 1% can be compacted by vibratory and impact methods. The disadvantage of compaction criteria based on grain size distribution is that soil samples have to be taken. It is preferable to use the results of the penetration tests for assessment of soil compatibility. Massarsch (1991) proposed compaction criteria for homogenous soils based on CPT cone resistance and friction ratio values as shown in figure In the case of thin layers of silt and clay, the effectiveness of soil compaction is reduced. Based on the data prepared in figure 3.19 and using Massarsch s method, it is shown that the thin layers of silt and clay are not compactable, and the sand layers are compactable. Using figure 3.18 for comparison between the CPT results before and after the DDC tests, it can be seen that the cone resistance and side friction increased at most penetration depths with a relatively even distribution. The friction ratio values along the depth are almost unchanged. The water table level did not change after compaction. From the analysis of the PCPT results, it can be drawn that the DDC tests were effective to improve the strength and deformation characteristics of the granular fill at station 11+. (2) Station Figure 3.2 presents the PCPT results for the backfill at station The backfill consists mainly of sands with a thin layer of silty sand located at a depth of about 15 ft. The ground water table level is located at a depth of about 12 feet from the surface. Figure 3.21 shows the soil identification of the backfill at station According to Massarsch s method (1991), the backfill is compactable. From the PCPT results presented in figure 3.2, following DDC, the cone resistance and local side friction were improved at most depths, and the water table level was lowered. Before the compaction, the water table level was at a depth of 12 ft below the ground surface and after the DDC it was at

7 a depth of 16 ft below the ground surface. The water table level was therefore lowered 4 ft by the compaction. (3) Station 141+ Figure 3.22 presents the PCPT results for the backfill at station From the soil profile provided in figure 3.23, the backfill consists mainly of sands, with thin layers of silt and clay. Using Massarsch s method (1991), the sand in the backfill is compactable or marginally compactable, and the silt or clay layers are not compactable. Comparison of the PCPT results before and after the DDC tests are shown in figure 3.22, suggesting that the cone resistance and local side friction of the backfill were improved at most depths and their distributions with the depth were more even. Before DDC, the water table level in the backfill was at a depth of about 4.3 feet from the ground surface, and after DDC, the water table level was lowered to the depth of 12 ft from the ground surface. (4) Station Figure 3.24 presents the PCPT results for the backfill at station Based on the data presented in figure 3.25 and using the method suggested by Robertson and Campanella (1983), the backfill consists mainly of sand with thin layers of silty sand. Before the DDC tests, the water table level in the backfill was at about 1 feet depth from the ground surface. The water table level was lowered to a depth of 18 ft below the ground surface after the compaction. Using Massarsch s method (1991), the backfill is totally compactable or marginally compactable. By comparing the PCPT results before and after the DDC tests as shown in figure 3.24, it can be noticed that cone resistance and local side friction of the backfill were improved at most locations by the DDC and their distributions along the depth were more even after the compaction. (5) Station Figure 3.26 presents the PCPT results for the backfill at station Based on the data presented in figure 3.27 and using the method suggested by Robertson and Campanella (1983), the backfill consists mainly of sand to silty sand with some thin layers of sandy silt or silt. Using the method suggested by Massarsch (1991), most of the silty sand and sandy silt to silt are not compactable. By comparing the PCPT results before and after the DDC compaction, it can be noticed that the cone resistance and local side friction were improved at most locations and their distributions along the depth became more even after the compaction. The water table level in the backfill did not change before and after the deep dynamic compaction and was located at a depth of about 4.2 feet from the ground surface. The water table level did not change in section because the sheet pile did not cut off the water flow path from the outside bogs, which supplements the loss of water in the backfill due to the deep dynamic compaction. By analyzing the PCPT results of the backfill at the five instrumented stations before and after the DDC, the following conclusions can be drawn: 1. According to the method suggested by Robertson and Campanella (1983), the backfill at the five instrumented stations consists mainly of sand to silty sand. At some stations, there were some thin layers of silt or clay. 2. According to the method suggested by Massarsch (1991), most of the backfill at the five instrumented stations consists of compactable or marginally compactable material, especially for those in the upper layers. 3. Based on the analysis of the PCPT data before and after the DDC, it can be concluded that following the compaction, the cone resistance and local side friction of the backfill was improved to depths ranging from 2 ft to 28 ft. The cone resistance was also found to provide quite uniform resistance within this depth. At stations 117+5, 141+, and the water table levels were 115

8 116 lowered by 4 ft to 8 ft as the water in the backfill had been expelled out by the compression effect induced by the DDC. At some stations 11+ and , there was no apparent water table level changes due to the free water flow path between the inside backfill and the outside water in the bogs. 4. It was proved that deep dynamic compaction (DDC) is an effective way to densify the soil hence improve the soil strength and deformation characteristics. The possibility of liquefaction in the backfill granular materials in earthquake was reduced Relative Density Relative density is difficult to measure in laboratory test because of the uncertainties involved with the natural density and the determination of the maximum and minimum densities (ASTM, 1973). The relationship between relative density, D r, and cone resistance, q c, are based primarily on calibration chamber test. The relationship between relative density, D r, and cone resistance, q c, of a sand is greatly affected by the sand s compressibility. For a given value of relative density and effective overburden pressure σ ' v, a sand of high compressibility has a lower q c than a sand of low compressibility. The relationship between relative density and cone resistance suggested by Jamiolkowski et al. (1985) was employed to estimate the relative density of the backfill. These relationships are applicable to relatively uniform, uncemented, clean, predominantly quartz sand. In a thin sand layer, an underestimation of D r may be obtained because the full cone resistance may not be have been developed. Based on Jamiolkowski et al. (1985): emax e qt Dr = = log1 (3.1) e '. max emin σ [ ] 5 ' 2 qc, σ v expressed in tons/ m. Figures 3.28 to 3.32 present the relative density, D R, and the dynamic shear modulus and constrained modulus of the backfill with depths at the five instrumented stations before and after DDC. It can be observed that after the deep compaction, the relative density values increased significantly, at some depths by close to 1%. After the DDC, the relative density distribution along the depth became more even than prior to the compaction, a testimony to the effectiveness of the deep dynamic compaction. It also can be observed that the deep compaction has a greater effect on the upper layers than on the deeper layers. After the dynamic compaction, the relative density of the backfill in the upper 2 ft layer was increased by 8 to 1%. However, for the backfill at depths of 2 ft below the ground surface and lower, the improvement was less than 8 percent Strength There are several possible methods to determine the effective angle of shear resistance based on the CPT data analysis. One is to use the relationship between the ' effective shear resistance angle, φ, and the relative density, D R, provided by Schmertmann (1978). Another approach is to use the Terzaghi bearing capacity factor for general shear, v

9 117 N γ, as an intermediate parameter. A correlation between N γ and q c is given by Muhs and Weiss (1971): N γ = 12.5.qt. This correlation was derived from a large-scale shallow footing test on sand, and it does not consider the overburden pressure. A direct correlation derived from a bearing capacity theory is developed by Mitchell and Durgunoglu (1975) using a soil cone friction angle equal to.5 φ ' ' and a lateral earth pressure coefficient, K = 1 sinφ, while ignoring the effects of soil compressibility. In highly compressible sands, φ ' may be significantly higher than that derived from the correlation suggested by Mitchell and Durgunoglu. If R f exceeds about.5%, the method developed by Mitchell and Durgunoglu is believed to underestimate φ ', because it takes no account of the curvature of the strength ' envelope. At higher confining pressures, φ is somewhat lower. The differences between the estimated and actual friction angle increase with the increase in the relative density in the following way (Jamiolkowski et al., 1985): D R <.35, to 1.35 < D R <.65 2 to 3.65 < D R <.85 3 to 5.85 < D R 5 to 8 Figures 3.33 to 3.37 present the range in the backfill internal friction angle φ ', with depth at the five instrumented stations, before and after the deep dynamic compaction. These results were based on the chart developed by Mitchell and Durgunoglu (1975), using a soilto-cone friction angle equal to.5φ and a lateral earth pressure coefficient, K ' = 1 sinφ. It can be noticed that at a lower overburden effective pressure, φ ' is somewhat higher than that calculation at higher overburden effective pressures. After the deep compaction, φ ' at different overburden effective pressure increases some, which prove that DDC is effective to improve granular materials strength. By comparing with table 3.2 and 3.3, it can be noticed that the laboratory measured peak effective shear resistance angle at different confining pressures fits well with the values from the PCPT data analysis Deformability Depending on the problems under consideration, it may be necessary to evaluate one of three moduli: the constrained modulus, M (which is equal to the reciprocal of the oedometer vertical coefficient of volume change, m v ), the Young s modulus, E, or the shear modulus G. Because stress-strain curves for sands are non-linear, it is necessary to fix a stress range over which the modulus is to be determined. (1) Constrained Modulus, (M) Correlations between constrained modulus, M, and cone resistance, q c, are commonly expressed as: M = α M. q c (3.2) where α M is often stated to be in the range 1.5 to 4. Vesic (197) suggested the relations: 2 DR α M = 2 1+ (3.3) 1

10 118 Others such as Parkin and Lunne (1982) developed α M values for NC sand based on pressure chamber tests. In practice, α M decreases with increasing q c, and α M increases with increasing stress level. Webb et al. (1982) suggested that M values should be calculated as follows: 2 M 2.5 q MN m (3.4) Clean sands: = ( c ) Clayey sands: M 1.7 ( q + 1.6) = c 2 MN m (3.5) Lunne and Christoffersen (1983) suggested another calibration for M. They proposed conservative values for the initial tangent constrained modulus, M, in NC sands and OC ' ' sands. Thus the constrained modulus applicable for the stress range σ v to σ v + Δσ can be estimated as: ' Δσ σ V V M = M ( ) (3.6) ' σ V The constrained modulus for the backfill at the five instrumented stations was estimated based on Vesic s relations described in equations 3.2 and 3.3. The variation of the backfill s constrained modulus (M) with depth at the five instrumented stations (before and after the DDC) are presented in figures 3.28 to It can be observed that the constrained modulus (M) varies little with the change in the overburden pressures. The constrained modulus increased substantially following the deep dynamic compaction, typically by 3 to 4 times the values that were at the same depth before the compaction. At stations 11+, 141+ and , the constrained modulus values of the backfill were improved by up to five times by the compaction, and at the stations and the constrained modulus values of the backfill increased to twice their values before the compaction. It indicated that DDC compaction is an effective way to improve the granular material deformation capacity. Under a given loading condition, the soil with a larger constrained modulus would have a smaller settlement than that with a smaller constrained modulus. Referring to Route 44 conditions, the above relations suggest that the settlements expected to ensue by the embankment construction would decrease as a result of the DDC and the increase in the constrained modulus. It also can be observed that the DDC compaction has a larger effect on the soils in the upper 2 ft compared to the soils at depths of over 2 ft below the surface. (2) Dynamic (Small Strain) Shear Modulus, (G) Dynamic shear modulus, G, is of great importance in soil dynamics and earthquake engineering. Based on laboratory tests, Robertson and Campanella (1983) provided the correlations between dynamic shear modulus, cone resistance, and vertical effective stress. Rix and Stokoe (1992) developed the following correlations between dynamic shear modulus, cone resistance, and effective overburden pressure: G 1634 qt = (3.7) ' q t σ v The dynamic shear modulus (G) of the backfill with depth at the five instrumented stations before and after the deep dynamic compaction were calculated based on the above relationship and are shown in figures 3.28 to Based on the information presented in the figures, a significant increase in the small strain modulus is observed in stations 141+ and.75

11 while a smaller increase is observed at the other three locations. At stations 11+, 117+5, 141+ and 143+5, the dynamic shear modulus values of the backfill after the compaction were about 1.3 to 2. times higher than the values prior to the compaction. At station , the dynamic shear modulus was almost doubled along the entire depth due to the DDC. (3) Young s Modulus, (E) For other than one-dimensional cases, Young s modulus, E, is used rather than the constrained modulus, M. As with M, E is dependent on the stress level. Based on pressure chamber tests, Robertson and Campanella (1983) suggested correlations for the secant Young modulus at 25% of the failure stress ( E 25 ) and at 5% of the failure stress ( E 5 ) for uncemented NC quartz sands. For most foundation problems, E 25 is relevant, although E 5 may be more relevant when considering end-bearing capacities of piles. Robertson and Campanella suggested that except at very low relative density, E 25 varies between about 1.5 q c and just over 2 q c. For OC sands, E 5 varies between 6 q c and 11 q c (Baldi et. al., 1982). Another common way to determine the Young s modulus E, is based on the dynamics shear modulus, G, using the relationship: E = 2G ( 1+ν ) (3.8) For soils, the value of Poisson ratio commonly ranges between.2 and.5. Using the method suggested by Robertson and Campanella (1983), the E 25 of the backfill was found to be 5 6 around 2. 1 psf before the compaction and psf after the compaction. For the 5 5 sand below the backfill, E was around 3. 1 psf before the compaction and 4. 1 psf after the compaction. Based on equation 3.8 and assuming ν equal to.25, the Young s 5 6 modulus E of the backfill was around 4. 1 psf before the compaction and psf 5 after the compaction. For the sand below the backfill, E was about psf before the 5 compaction and psf after the compaction. It was noticed that the dynamic compaction had much greater effect on the backfill than on the sand below it. Tables 3.4 to 3.7 summarize the engineering parameters of the backfill and deep sand deposits based on the PCPT field tests before and after the deep dynamic compaction Summary Based on the laboratory and PCPT tests on the backfill material at Route 44, the following conclusions are derived: 1. The backfill at the five instrumented stations of Route 44 at Carver MA consists mainly of fine to coarse compactable sand. Based on the information provided by the PCPT, at some stations there are also very thin layers of silt or clay. 2. From the triaxial and direct shear tests on the backfill, the measured peak strength parameters are very similar. From the direct shear test, the peak friction angle is 41. and the residual friction angle is 36.. From the triaxial test, the measured peak and residual friction angles are 38.9 and 29. respectively. 3. From the PCPT results, local side friction and pore pressure before and after the DDC were measured and compared. The engineering parameters of the backfill along penetration depths of 8 ft to 25 ft were obtained. It is shown that DDC

12 12 compaction is an effective way for improving the backfill strength and deformation capacities. Following two passes of the deep dynamic compaction (DDC), the relative density D r of the backfill was improved by 8 to 1 percent and the values of the dynamic shear, constrained and Young s moduli were twice the values before the compaction. 3.7 ORIGINAL SHEET PILE DESIGN Assumed Conditions The original sheet pile design was performed by Geosciences Testing And Research, Inc. (GTR) of North Chelmsford, Massachusetts. Section 3.7 is therefore based on the report entitled Route 44 Relocation Cantilever Sheeting Design Phase 1 and 2 Carver, Massachusetts by Chernauskas and Paikowsky (21). A mechanically stabilized earth (MSE) wall is proposed for the support of the relocated highway in phase 1 and 2 area. In order to build the MSE wall, the existing peat/muck must be excavated and replaced with granular fill. A combination of vibrocompaction and deep dynamic compaction (DDC) is proposed to compact the fill. Steel sheet piling, supported by cantilever methods, will be used to stabilize the highway alignment during the excavation and fill placement procedures. The steel sheet piling will be left in place and capped after the MSE wall is built. It was assumed that vibrocompaction will be used to compact the soil between the sheeting and MSE wall (on both sides) and the area directly under the MSE will be compacted using DDC methods. Steel sheeting (ASTM A572 Grade 5) consisting of PZ22 and PZ27 sections is required along the sheeting alignments. The lengths of the sheeting vary between 25 and 55 feet, depending on the depth to the bottom of the peat, final grade inside and outside the sheeting, water level, distance to the MSE wall, and the height of the MSE wall Design Procedures The methodology used to carry out the sheeting design is: 1. Evaluation of the various stages of construction. 2. Review of soil data and geometry along each sheeting alignment at each station. Development of simplified profiles for cantilever sheeting analyses and identify grade inside and outside sheeting, top of roadway, bottom of peat, water elevation and MSE wall height and distance from sheeting. 3. Evaluation of the surcharge pressures developed on the sheeting from the MSE wall. 4. Use a computer program (Prosheet) to analyze the sheeting for all possible loading design cases. 5. Estimate the deflections of the sheeting and the corresponding settlements behind the sheeting. Expansion of the above follows: 1. The stages of construction were identified over the course of the project. The primary stages with regard to the performance of the cantilever sheeting system include:

13 121 a. Stage I Install sheeting. b. Stage II Excavate peat/muck. A minimum excavation of 5 feet was assumed in cases where peat/muck was not identified. The maximum excavation approached 3 ft in some areas. The depth of excavation was referenced to the grade just outside the sheeting. c. Stage III Place loose granular fill to the top of the sheeting. The backfill was assumed to be placed three feet above water level or at the final grade inside and next to the sheeting, whichever was higher. This grade extends from the sheeting to the MSE wall location. d. Stage IV Perform Vibrocompaction (within 2 to 25 feet of the sheeting). Prepare final grade after vibrocompaction using conventional compaction methods. This grade was usually 1 to 2 feet lower than the vibrocompaction working grade. e. Stage V Build MSE wall. f. Stage VI Grade road and cap sheeting. 2. Typical profiles along each sheeting alignment were developed from the boring logs, and profiles available in the geotechnical report and the contract documents. The data associated with the stage of construction was compiled as follows: Stage II Thickness of peat (depth of excavation). Stage III Compaction fill height. Stage IV Final fill height. Stage V MSE wall height above final inside grade (above stage IV). 3. The surcharge imposed on the sheeting from the construction of the MSE wall was evaluated using Boussinesq s elastic theory for strip loading. A unit weight for the fill material was assumed to be 12 pounds per cubic foot, strip width of 45 feet, and distance to sheeting of 2 or 25 feet (depending on stationing) were used in the analyses. A Poisson s ratio of.5 was used for calculation. 4. The elevation of the top of the sheeting must start at the final grade inside the sheeting or 3 feet above the water table, whichever is higher. The vibrocompaction working grade was assumed to be at least 3 feet higher than the water level elevation and extends from the sheeting to the MSE wall location. The water level was taken from the levels provided in the Geotechnical report soil profiles. If the water levels vary from those assumed, the lengths and deflections of the sheeting will differ from those determined in these analysis. The water levels encountered during construction will be reviewed if they are different from those assumed in the analyses. The final sheeting lengths are slightly longer than those necessary from the analysis (up to 5 feet longer) to account for sufficient penetration below the bottom of the backfill (i.e. tip of vibroprobe does not extend near the tip of the sheet to minimize disturbance of the passive resistance on the other side). 5. The predicted greatest deflections during excavation occurs in those areas that have 2 feet or more of peat (deflection are typically between 1 and 1 inches). The greatest additional deflections during the construction of the MSE wall occurs in those areas that have 2 feet or more of peat, are within 2 feet of the MSE wall, or have MSE wall heights greater than 2 feet (additional deflections are typically between 1 and 1-1/2 inches).

14 122 The sheeting may experience deflections of 1 to 3 inches beyond those shown for stage V if construction loads occur close to the sheeting. For this reason, construction equipment, stockpiling, etc., should not be located within 15 feet of the sheeting. The additional deflection of the sheeting after stage V due to bog access road traffic may approach 1 inch, although this is conservative as the loads were assumed to be permanent even though they are temporary. The influence of the deflection of the sheeting on the settlement under the MSE wall was investigated using empirical relationships developed by Clough and O Rourke (199) and Goldberg et al. (1976). For sandy materials, the MSE wall is outside the settlement zone influenced by lateral wall deflection at the permanent sheeting line in all cases. If still clay is assumed, which can be considered as the worst case scenario, the MSE wall between stations 96+5 and 11+5 (only 2 feet from the sheeting) may experience settlement (and possibly differential settlement) of around 1 inch Final Design 1) PZ22 and PZ27 or equivalent (Grade 5) sheeting can be used across the site during excavation, to retain the fill during Vibrocompaction, and in the permanent condition. Sheeting lengths of 25 to 55 feet are necessary. Refer to table 3.8 for the lengths and sizes of the sheeting corresponding to the station locations. The compaction fill height must be added to the outside sheeting elevation (both provided in table 3.9) to obtain the top of the sheeting elevation at each station location. If the top of sheeting elevation varies from that determined from table 3.9, then the analysis should be reviewed. 2) Estimated sheeting deflections of 1 to 1-1/2 inches may occur during construction of the MSE wall. The MSE wall, however, is located outside the settlement zone influenced by lateral wall deflection at the permanent sheeting line (according to Clough and O Rourke (199) and Goldberg et al. (1976)). Under the worst conditions, differential settlement of up to 1 inch may occur under the MSE wall, particularly between stations 96+5 and 11+5 left. Although the preliminary calculations indicate that lateral deflections from the sheeting either do not influence the settlement under the MSE wall or are only minimal, the designer should evaluate this issue more thoroughly. 3) Cranes or other construction loads should not be located within 15 feet of the sheeting to limit deflections after the MSE walls are constructed. Estimated additional deflections of 1 to 3 inches may occur if these construction loads are placed close to the sheeting after stage V begins. Deflections of up to 1 inch may occur due to the light bog access road traffic. 4) The performance of the sheeting is critical with regard to the water level. A net change in water level such that it is higher between the sheets than in the bog/wetland can significantly decrease the stability and increase the deflections of the sheeting. This is of particular importance during the permanent condition. If there is a possibility of different water levels inside and outside the sheeting, then measures such as cutting weep holes in the sheeting can be implemented to allow water to pass through.

15 5) The sheeting should be monitored to record deflections during the various stages of construction, particularly in the deep peat and high MSE wall areas. The sheeting should be measured for lateral deflections at each station and half station location. The measurements should be taken according to the following schedule: a) Before Stage II (zero reading). b) Midway and end of Stage II. c) Midway and end of Stage III. d) End of Stage III. e) Beginning of Stage V, upon 25%, 5%, and 75% completion of the MSE wall, and after completion of the MSE wall. 6) If the observed deflections at any time exceed the values estimated herein in table 3.8 and 3.1 at each stage, designers (GTR) must be notified in order to evaluate existing conditions and prepare mitigating procedures to limit further deflections. Some methods to reduce the deflections can include: a) Driving soldier piles adjacent to the sheeting in deep peat areas to increase stiffness. b) Reduce the working grade. c) Reduce the final grade. All the analyses are based on available information from the contract documents. The inspection of the field work regarding the compaction and excavation support system (i.e. excavation, installation, and support survey monitoring) will be performed by others. Excavation, installation, and support system monitoring should be coordinated prior to the start of construction to ensure that all activities and phases of the earth support system installation occur as described in our recommendations or in the drawings/project specifications. If conditions or procedures in the field vary from those assumed here, then GTR will need to review and revise its calculations accordingly. 123

16 124 Table 3.1 Summary of index properties and engineering parameters of Carver peat Parameter Model Soil unit weight below water table level Name/Symbol Units Magnitudes Notes γ sat (lb/ft 3 ) 66.4 Bulk unit weight test (Elsayed,23) Specific gravity G S (Elsayed, 23) Permeability in 3 Permeability test Horizontal K x (ft/day) (Elsayed, 23) direction Permeability in Permeability test K Vertical direction y (ft/day).33 (Elsayed, 23) Cohesion C (constant) ref (lb/ft 2 Triaxial Test ) 41.7 (Elsayed, 23) Triaxial Test Friction angle φ ( ) 12 (Elsayed, 23) Compression index C C Oedometer test (Elsayed, 23) Swelling index C S Oedometer test (Elsayed, 23) Secondary Oedometer test C α compression index (Elsayed, 23) Water content ϖ (%) 759~95 (Elsayed, 23) Liquid limit L.L (%) 59 (Elsayed, 23) Plastic limit P.L (%) 39 (Elsayed, 23) Initial void ratio e ini Consolidation test (Ernst et al., 1996) Table 3.2 Summary of the triaxial test results of the backfill soil at route 44 Parameter σ c (psi) γ t (pcf) φ (degree) E i E 5 E failure Sample psi 2673 kpa 11 psi 758 kpa 3 psi kpa Sample psi 2673 kpa psi 752 kpa psi 2658 kpa Sample psi 2673 kpa 147 psi 113 kpa 84 psi kpa Average N/A psi 2673 kpa 122 psi 844 kpa 59 psi 354 kpa

17 125 Table 3.3 Summary of the direct shear test results of the backfill soil Test Number γ d pcf kn/m 3 Strain Rate mm/min Normal Stress psi kpa Shear Stress psi kpa Test 1 S Test 2 S Test 3 S Test 4 S Test 5 S Test 6 S Void Ratio φ φ p R τ 1 p = tan σ p 1 τ R = tan σ R Table 3.4 Summary of the engineering properties of the backfill before deep dynamic compaction (DDC) Parameter Name/Symbol Units Magnitudes Notes Relativity density D r (%) 65 PCPT test before DDC Soil unit weight below water table level Permeability in horizontal direction Permeability in vertical direction Dynamic (small strain) shear modulus γ sat (lb/ft 3 ) 12 PCPT test before DDC K x (ft/day) 3. K y (ft/day) 3. Dissipation test (PCPT) before DDC Dissipation test (PCPT) before DDC G (lb/ft 2 5 ) PCPT test before DDC Young s modulus E (lb/ft 2 5 ). 1 4 = 2G( 1+ν ) E & TC, Cohesion C (lb/ft 2 ) TC test, DS test Friction angle φ ( ) 32 PCPT test before DDC

18 126 Table 3.5 Summary of the engineering properties of the backfill after deep dynamic compaction (DDC) Parameter Name/Symbol Units Magnitudes Notes Relativity density D r (%) 9 PCPT test after DDC Soil unit weight below water table level Permeability in horizontal direction Permeability in vertical direction Dynamic (small strain) shear modulus γ sat (lb/ft 3 ) 131 PCPT test after DDC K x (ft/day) 2. K y (ft/day) 2. Dissipation test (PCPT) after DDC Dissipation test (PCPT) after DDC G (lb/ft 2 6 ).84 1 PCPT test after DDC Young s modulus E (lb/ft 2 6 ) = 2G( 1+ν ) E & TC, Cohesion C (lb/ft 2 ) TC test, DS test Friction angle φ ( ) 44 PCPT test after DDC Table 3.6 Summary of the engineering properties of the deep sand before deep dynamic compaction (DDC) Parameter Name/Symbol units Magnitudes Notes Relativity density D r (%) 65 PCPT test before DDC Soil unit weight below water table level Permeability in horizontal direction Permeability in vertical direction Dynamic (small strain) shear modulus γ sat (lb/ft 3 ) 126 PCPT test before DDC K x (ft/day) 3.3 K y (ft/day) 3.3 Dissipation test (PCPT) before DDC Dissipation test (PCPT) before DDC G (lb/ft 2 5 ) PCPT test before DDC Young s modulus E (lb/ft 2 5 ) E = 2G( 1+ν ) Cohesion C (lb/ft 2 ) TC test, DS test Friction angle φ ( ) 37 PCPT test before DDC

19 127 Table 3.7 Summary of the engineering properties of the deep sand after deep dynamic compaction (DDC) Parameter Name/Symbol units Magnitudes Notes Relativity density D r (%) 7 PCPT test after DDC Soil unit weight below water table level Permeability in horizontal direction Permeability in vertical direction Dynamic (small strain) shear modulus γ sat (lb/ft 3 ) 128 PCPT test after DDC K x (ft/day) 2.2 K y (ft/day) 2.2 Dissipation test (PCPT) after DDC Dissipation test (PCPT) after DDC G (lb/ft 2 5 ) PCPT test after DDC Young s modulus E (lb/ft 2 5 ) E = 2G( 1+ν ) Cohesion C (lb/ft 2 ) TC test, DS test Friction angle φ ( ) 38 PCPT test after DDC

20 128 Table 3.8 Route 44 relocation phase 1 and 2 cantilevered sheeting analysis summary of results (Chernauskas and Paikowsky, 21) Station Estimated Estimated Additional Sheeting Maximum Sheeting Deflection Deflection during MSE Length Stress Type After excavation wall construction (feet) (ksi) (inches) (inches) 96+5 to 99+5 L PZ ~ 1/ TO 11+5L PZ ~ to 147+5L PZ to 154+L PZ ~ ½ 154+ to 158+L PZ ~ to 162+5L PZ ~ to 13+ R PZ /2 1-1/2 13+ to 18+5R PZ ~ 1/ to 118+5R PZ ~ to 138+R PZ ~ to 142+5R PZ / to 143+5R PZ ~ ½ to 153+5R PZ <1/2 ½ to 157+5R PZ / to 161+R PZ ~ 1/2 Notes: 1. All sheeting is ASTM A572 Grade 5 steel. 2. The sheeting length is based on the longest length required from the worst case stage. In addition, the sheeting lengths are typically a few feet longer than required to ensure that the tip of the sheeting is at least 1 feet below the bottom of the backfill material. The elevation of the top of the sheeting must start at the final grade or 3 feet above the water table, whichever is higher. 3. The maximum stress is the highest stress developed in the sheeting over the course of all stages. 4. Represents the estimated deflection after peat/muck excavation. 5. Represents the estimated additional deflection experienced by the sheeting during the construction of the MSE wall. The sheeting may experience deflection of 1 to 3 inches beyond those shown if construction loads occur within 15 feet of the sheeting after stage V begin. The additional deflection of the sheeting after stage V due to the bog access road traffic may approach 1 inch. 6. No deflection after MSE wall construction due to grade outside sheeting at the same elevation as final grade inside sheeting.

21 Station Wall Drawing Boring Table 3.9 Route 44 relocation phase 1 and 2 left summary of sheeting data (Chernauskas and Paikowsky, 21) Grade Outside Sheeting (feet) Grade inside Sheeting (feet) Leveling Pad EL (feet) Top of Road EL (feet) Existing Grade (feet) Water Level (feet) Bottom of peat EL (feet) Stage II thickness of peat (feet) Stage III compaction fill height (feet) Stage IV final fill height (feet) Stage V Wall height above inside grade (feet) 965 W3 525 PWB W3 526 PWB W3 527 PWB W3 528 WB W3 529 WB W3 53 WB W3 531 WB W3 532 WB W3 533 WB W3 534 WB W3 535 PWB W6 617 WB W6 618 WB W6 619 WB W6 621 WB W6 621 WB W6 622 WB W6 623 WB W6 624 WB W6 625 HB465F W6 626 HB465F W6 627 PWB W6 628 PWB W6 629 PWB W6 63 WB W6 631 WB Distance from MSE wall (feet) 129

22 Table 3.9 Route 44 relocation phase 1 and 2 left summary of sheeting data (Chernauskas and Paikowsky, 21) (cont d) Station Wall Drawing Boring Grade Outside Sheeting (feet) Grade inside Sheeting (feet) Leveling Pad EL (feet) Top of Road EL (feet) Existing Grade (feet) Water Level (feet) Bottom of peat EL (feet) Stage II thickness of peat (feet) Stage III compaction fill height (feet) Stage IV final fill height (feet) Stage V Wall height above inside grade (feet) 15 W6 632 WB W6 633 WB W6 634 WB W6 635 WB W6 636 WB W6 637 WB W6 638 WB W6 639 PWB W6 641 WB W6 642 WB W6 643 WB W6 644 WB W6 645 WB W6 646 WB W6 647 WB W6 648 WB W6 649 WB W6 65 WB W6 651 WB W6 652 WB W6 654 PWB W6 655 PWB W6 656 WB W6 657 WB Distance from MSE wall (feet) 13

23 131 Table 3.1 Route 44 relocation phase 1 and 2 left cantilevered sheeting analysis input and results (Chernauskas and Paikowsky, 21) Cases Station Stage Cut/Fill surcharge Water depth below sheet top (feet) Sheeting type Sheeting length (feet) Maximum Stress (ksi) Estimated Deflection (inches) 7A II 25 5 PZ / B III 7 5 PZ /2 ~ 7C 13+ IV 5 5 PZ <1/2 7D (R) V 2 MSE 5 PZ /2 7E VI 25psf adj. 5 PZ /2 8A 13+ II 5 4 PZ <.1 ~ 8B ~ III 7 4 PZ C 18+5 IV 5 4 PZ <1/2 8D (R) V 19 MSE 4 PZ /2 9A II 1 5 PZ ~ 9B III 7 5 PZ ~ 9C IV 5 5 PZ <1/2 9D (R) V 29 MSE 5 PZ E VI 25 psf adj. 5 PZ /2 1A II 5 5 PZ22 11 <.1 ~ 1B ~ III 5 5 PZ ½ 1C 138+ IV 5 PZ D (R) V 18 MSE 5 PZ A II 3 6 PZ /2 11B 138+ III 7 6 PZ ~ 11C IV 5 6 PZ <1/2 11D (R) V 13 MSE 6 PZ E VI 25 psf 6 PZ A II 5 6 PZ <.1 ~ 12B ~ III 7 6 PZ /2 12C IV 5 6 PZ <1/2 12D (R) V 8 MSE 6 PZ /2 13A II 1 9 PZ <1/2 13B ~ III 7 9 PZ C IV 6 9 PZ ½ 13D (R) V 1 MSE 9 PZ A II 25 6 PZ /2 14B ~ III 7 6 PZ /2 14C IV 6 PZ D (R) V 17 MSE 6 PZ A II 1 5 PZ ~ 15B ~ III 5 5 PZ C 161+ IV 5 5 PZ D (R) V 17 MSE 5 PZ /2

24 132 Figure 3.1 View of the completed embankment and sheet piles with concrete cap around station 11+ R

25 133 ROUTE 44 SUBSURFACE PROFILE Kingston GROUND SURFACE ROUTE 44 PROFILE Plymouth Plymouth Carver P A-2-4* K-1-17 C-4-21 P P A-2-4 A-2-4 A-2-4 Wall 8 A-3* SECTION II SECTION I A-4 A-3 A-2-4 A-1-b AASHTO soil type at test pit location A-1-b A-2-4 Walls 5, 6 & 7 A-3 A-3* A-1-b* A-1-b* Wall 4A A-1-b A-1-b* GROUNDWATER GRANULAR SOILS BOTTOM OF PEAT BOGS TOP OF ROCK ROCK CORE LOCATIONS STATION (FT) Figure 3.2 Geologic profile of route 44 C-4-2 A-4 A-4 GRANITE 12 Walls 3 & 4 A-1-b 1 C-4-18 C-4-19 Walls 1 & 2 A-3 A-2-4 A-2-4 SILTSTONE A-1-b ELEVATION (FT)

26 station 11+(R) station 117+5(R) Top of Proposed Wall WB-21 PWB-7 WB-234 W-215 PWB-9 WB-217 HB-456F WB-219 PWB-1 WB-221 PWB-11 WB-224 W-225 WB-226UD PWB-12 Existing Ground Surface 11 WB-213UD BOG DAM 1 HB-459F HB-461F PEAT PEAT ELEVATION, FT 9 PEAT FINE TO COARSE SAND (to elevation 3 ft) Distance between stations is 1 ft BORING LENGEND 13 N SPT#'S 2 US Undisturbed Sample GWE@Time of Boring GWE@Wells and Bogs PEAT PROBE Water table level WOH Weight of Hammer WOR Weight of Rods Figure 3.3 Subsurface Cross-section from station 98+ (R) to 119+ (R) including the instrumented station 11+ (R) and (R)

27 Top of Proposed Wall 12 WB-232 WB-234UD WB-237 Fine to Coarse Sand (to elevation 2 ft) PWB-16 Existing Ground Surface WB-23 2/6'' PWB /6'' 1/18'' WB /12'' Distance between stations is 1 ft BORING LENGEND 13 N SPT#'S 2 GWE@Time of Boring PEAT PROBE US Undisturbed Sample GWE@Wells and Bogs Water table level WOH Weight of Hammer WOR Weight of Rods /6'' 7/6'' 16/6'' 48 9/6'' /18'' 1/6'' WOH/6'' WOH/6'' WOR/6'' WOR/24'' US 1/18'' US PEAT station 141+(R) Figure 3.4 Subsurface cross-section from station 135+ (R) to 147+ (R) including the instrumented station 141+ (R) ELEVATION, FT (1ft=.348m)

28 Station 143+5(L) Top of Proposed Wall PWB WB WB /6'' 1 7 WB /6'' BOG DAM WB-239 1/12'' WOH/6'' WOH/6'' 1/36'' PEAT WB-242 WOH/54'' WOH/6'' WOH/48'' HB-465F WOH/18'' PWB-17 7 R 5 23 Existing Ground Surface WB-245 WB-246 WOH/18'' WOH/18'' WOH/12'' 6/6'' FINE TO COARSE SAND (to elevation 1 ft) Distance between stations is 1 ft BORING LENGEND 13 2 N SPT#'S WOH GWE@Time of Boring GWE@Wells and Bogs PEAT PROBE Water table level Weight of Hammer Figure 3.5 Subsurface cross-section from station 138+ (L) to 152+ (L) including instrumented station (L) ELEVATION, FT (1 ft=.348m)

29 Top of Proposed Wall HB-466F 12 WB-27 station (R) Existing Ground Surface 6 PWB-18 WB-257 WB-261 WB-262 WB-263 WB ELEVATION, FT WOH/48'' WOH/3'' P Fine to Coarse Sand (to elevation 18 ft) P P P /6'' 14 PEAT P P /6'' P Distance between stations is 1 ft BORING LENGEND 13 N SPT#'S 2 US Undisturbed Sample GWE@Time of Boring GWE@Wells and Bogs PEAT PROBE Water table level WOH Weight of Hammer WOR Weight of Rods 5 Figure 3.6 Subsurface cross-section from station 149+ (R) to 159+ (R) including the instrumented station (R)

30 138 SCALE IN FEET BOG LEFT OF ROUTE 44 Section 143+5(L) WB PWB-7 Section 11+(R) BOG PWB WB-214 WB-213UD W-225 HB-461F Section 117+5(R) PWB-12 WB-226UD WB-234UD WB Section 141+(R) WB-237 WB BOG WB WB-261 WB WB-262 Section (R) BOG RIGHTT OF ROUTE 44 HB Highway Control Boring WB Retaining Wall Control Boring PWB Pilot Wall Boring W Monitoring Well Type Figure 3.7 Plane view of route 44 Carver Massachusetts including the instrumented sections and related borings

31 139 Figure 3.8 Tube used for peat sampling (Elsayed, 23) Figure 3.9 Peat sampling in cranberry bog (Elsayed, 23)

32 14 Figure 3.1 Extruded wet peat sample (Elsayed, 23) U.S. standard sieve sizes Cobble Gravel Sand Coarse to medium Fine Silt Clay 1 1 inch 3/8 inch No.4 No.1 No.4 No.1 No.2 9 Grain size distribution Curve (sand sample from Route 44) Boundary for Most Liquefiable Soil 2 Boundary for Potenially Liquefiable soil (TSUCHIDA, 197) Percent finer by weight D D 1 3 D Diameter (mm) Figure 3.11 Sieve analysis of the backfill material at route 44, Carver MA

33 Deviator Stress (psi) (1 psi = kpa) s c = 4.2 psi g t = 125 pcf s c = 12.5 psi g t = pcf s c = 8.3 psi g t = 126 pcf Axial Strain (%) Figure 3.12 Stress-strain curve from triaxial tests on the backfill soil at Route 44 in Carver

34 t (psi) (1 psi = kpa) Φ = 38.9 s c = 8.3 psi g t = 126. pcf s c = 12.5 psi g t = pcf 5 s c = 4.2 psi g t = 125. pcf s (psi) (1 psi = kpa) (a) 4 35 t (psi) (1 psi = kpa) Φ = 29. s c = 12.5 psi g t = pcf 5 s c = 4.2 psi g t = 125. pcf s c = 8.3 psi g t = 126. pcf s (psi) (1 psi = kpa) (b) Figure 3.13 Mohr-circle of the triaxial samples at (a) failure and the failure envelope of the backfill soil, and (b) the residual state and the residual failure envelope of the backfill soil

35 143 Shear Displacement (inch) (1 inch =.254 m) t/s t/s Normal Stress 3.2 psi 7.1 psi 9. psi 9.28 psi 8.55 psi psi Shear Stress (psi) (1 psi = kpa) Shear Displacement (inch) (1 inch =.254 m) Shear Displacement (inch) (1 inch =.254 m) Figure 3.14 Stress-strain curves of direct shear tests on backfill soil Normal Displacement (inch) (1 inch =.254 m)

36 144 Normal Stress (psi) (1 psi = kpa) Normal Stress (psi) (1 psi = kpa) Shear Stress (psi) (1 psi = kpa) F P =41 F R = Shear Stress (psi) (1 psi = kpa) Normal Stress (psi) (1 psi = kpa) Normal Stress (psi) (1 psi = kpa) (a) peak failure (b) residual state Figure 3.15 Relationship between normal stress and shear stress obtained by direct shear tests of the backfill soil Figure 3.16 Configuration of a typical cone penetration test (website of Frugo, Inc.)

37 145 Figure 3.17 Various cone configurations (website of Frugo, Inc.) Cone resistance, q c (tsf) Local side friction, f s (tsf) Pore pressure, u (tsf) Friction ratio, R f =f s.1/q c (%) Sta Silty Sands Sands Silty Sands Clayey Silts Before DDC After DDC Before DDC After DDC 1 ft =.348 m 1 tsf = 95.7 kpa Before DDC After DDC Sands Depth (feet) Depth (feet) Silty Sands 2 22 Hydraustatic Before DDC After DDC Sands Cone resistance, q c (tsf) Local side friction, f s (tsf) Pore pressure, u (tsf) Friction ratio, R f =f s.1/q c (%) Figure 3.18 PCPT results including profiling and soil identification for the backfill material at station 11+, route 44 in Carver, MA

38 146 Cone resistance, q c (MN/m 2 ) Friction ratio, R f (%) compactable Sands Silty Sands marginally compactable Sta.11+ (Soil classification from Robertson and Campanella,1983) (Soil classification for DDC, Massarsc, 1991) before DDC after DDC Sands Silts and Silts not compactable Clayey Silts and Silty Clay Clay Peat Cone resistance, q c (MN/m 2 ) Friction ratio, R f (%) Figure 3.19 Soils identification of the backfill at station 11+ Sta Cone resistance, q c (tsf) Local side friction, f s (tsf) Pore pressure, u (tsf) Friction ratio, R f =f s.1/q c (%) Initial After DDC Initial After DDC 1 ft =.348 m 1 tsf = 95.7 kpa Initial After DDC Initial After DDC Sand Depth (feet) 12 (before DDC) 12 Depth (feet) Silty Sand (after DDC) Hydraustatic (before DDC) Sand Hydraustatic (after DDC) Cone resistance, q c (tsf) Local side friction, f s (tsf) Pore pressure, u (tsf) Friction ratio, R f =f s.1/q c (%) Figure 3.2 PCPT results including profiling and soil identification for the backfill material at station 117+5, route 44 in Carver, MA 22 24

39 Friction ratio, R f (%) compactable Sands Sta.117+ (Soil Classification from Robertson and Campanella,1983) (Soil Classification for DDC from Massarch, 1991) before DDC after DDC Cone resistance, q c (MN/m 2 ) Silty Sands marginally compactable Sands Silts and Silts not compactable Clayey Silts and Silty Clay Clay Peat Cone resistance, q c (MN/m 2 ) Friction ratio, R f (%) Figure 3.21 Soils identification of the backfill at station Cone resistance, q c (tsf) Local side friction, f s (tsf) Pore pressure, u (tsf) Friction ratio, R f =f s.1/q c (%) Sta Gravelly sand to sand (before DDC) ft =.348 m 1 tsf = 95.7 kpa Clean sand to silty sand 8 8 Silty sand to sandy silt Clean sand to silty sand 12 Silty sand to sandy silt (after DDC) 12 Clean sands to Silty sand Depth (feet) 16 2 Initial After DDC Initial After DDC Hydraustatic (before DDC) Initial After DDC Initial After DDC 16 2 Depth (feet) Silty sand to sandy silty24 Clay to silty clay Clean sand to silty sand Clayey silt to silty clay Hydraustatic (after DDC) Clean sand to sandy silt Cone resistance, q c (tsf) Local side friction, f s (tsf) Pore pressure, u (tsf) Friction ratio, R f =f s.1/q c (%) Figure 3.22 PCPT results including profiling and soil identification for the backfill material at station 141+, route 44 in Carver, MA 4

40 148 Friction ratio, R f (%) compactable Sands Sta.141+ (Soil Classification from Robertson and Campanella,1983) (Soil Classification for DDC from Massarch, 1991) before DDC after DDC Cone resistance, q c (MN/m 2 ) Silty Sands marginally compactable Sands Silts and Silts not compactable Clayey Silts and Silty Clay Clay Peat Cone resistance, q c (MN/m 2 ) Friction ratio, R f (%) Figure 3.23 Soils identification of the backfill at station 141+ Sta Sand 2 Cone resistance, q c (tsf) Local side friction, f s (tsf) Pore pressure, u (tsf) Friction ratio, R f = f s.1/q c Silty Sand Sand 8 1 (before DDC) Initial After DDC 8 1 Silty Sand Depth (feet) Initial After DDC (after DDC) Initial After DDC Initial After DDC Depth (feet) Hydraustatic (before DDC) 22 Sand ft =.348 m 1 tsf = 95.7 kpa Hydraustatic (after DDC) Cone resistance, q c (tsf) Local side friction, f s (tsf) Pore pressure, u (tsf) Friction ratio, R f = f s.1/q c Figure 3.24 PCPT results including profiling and soil identification for the backfill material at station 143+5, route 44 in Carver, MA 3

41 149 Friction ratio, R f (%) compactable Sands Sta (Soil Classification from Robertson and Campanella,1983) (Soil Classification for DDC from Massarch, 1991) before DDC after DDC Cone resistance, q c (MN/m 2 ) Silty Sands marginally compactable Sands Silts and Silts not compactable Clayey Silts and Silty Clay Clay Peat Cone resistance, q c (MN/m 2 ) Friction ratio, R f (%) Figure 3.25 Soils identification of the backfill at station Sta Cone resistance, q c (tsf) Local side friction, f s (tsf) Pore pressure, u (tsf) Friction ratio, R f =f s.1/q c Sand 2 1 ft =.348 m 1 tsf = 95.7 kpa Sand to silty sand 6 8 Silty sand to sandy silt Initial After DDC Initial After DDC Initial After DDC Initial After DDC 6 8 Sandy silt to clayey silt Depth (feet) Depth (feet) Silty sand to sandy silt 14 Hydraustatic Sand to silty sand Cone resistance, q c (tsf) Local side friction, f s (tsf) Pore pressure, u (tsf) Friction ratio, R f =f s.1/q c Figure 3.26 PCPT results including profiling and soil identification for the backfill material at station , route 44 in Carver, MA 2

42 15 Friction Ratio, R f (%) compactable Sands Sta (Soil Classification from Robertson and Campanella,1983) (Soil Classification for DDC from Massarch, 1991) before DDC after DDC 2 Cone Resistance, q c (MN/m 2 ) Silty Sands marginally compactable Sands Silts and Silts not compactable Clayey Silts and Silty Clay Clay Peat Cone Resistance, q c (MN/m 2 ) Friction Ratio, R f (%) Figure 3.27 Soils identification of the backfill at station Station 11+ Silty Sands Sands 2 Relative density, Dr (%) ft =.348 m 1 tsf = 95.7 kpa Dynamic shear modulus, G (MPa) Constrained modulus, M (MPa) M (before DDC) M (after DDC) 2 Silty Sands Clayey Silts Sands Depth (feet) Depth (feet) Silty Sands Sands Dr(before DDC) Dr(after DDC) G (before DDC) G (after DDC) Relative density, Dr (%) Dynamic shear modulus, G (MPa) Constrained modulus, M (MPa) Figure 3.28 Comparison of relative density, dynamic shear modulus and constrained modulus before and after deep dynamic compaction (DDC) at station 11+, Rt. 44

43 151 Station R Relatively density, Dr (%) Dynamic shear modulus, G (MPa) Constrained modulus, M (MPa) ft =.348 m 1 tsf = 95.7 kpa Sands Depth (ft) Silty Sands before DDC After DDC Depth (ft) Sands before DDC after DDC before DDC after DDC Relatively density, Dr (%) Dynamic shear modulus, G (MPa) Constrained modulus, M (MPa) Figure 3.29 Comparison of relative density, dynamic shear modulus and constrained modulus before and after deep dynamic compaction (DDC) at station 117+5, Rt Station 141+ R Gravelly Sands to Sands Relative density, Dr (%) Dynamic shear modulus, G (MPa) ft =.348 m 1 tsf = 95.7 kpa Constrained modulus, M (MPa) Clean Sands to Silty Sands 1 Silty Sands to Sandy Silt Clean Sands to Silty Sands Silty Sands to Sandy Silt Clean Sands to Silty Sands Depth (ft) 2 2 Depth (ft) Silty Sands to Sands Silt Clay to 25 Silty Clay Clean Sands to Silty Sands 25 Clayey Silt to Silty Clay 3 3 Clean Sand to Sandy Silt before DDC after DDC before DDC after DDC before DDC after DDC Relative density, Dr (%) Dynamic shear modulus, G (MPa) Constrained modulus, M (MPa) Figure 3.3 Comparison of relative density, dynamic shear modulus and constrained modulus before and after deep dynamic compaction (DDC) at station 141+, Rt. 44

44 152 Station L Sands Relative density, Dr (%) Dynamic shear modulus, G (MPa) before DDC after DDC Constrained modulus, M (MPa) Silty Sands ft =.348 m 1 tsf = 95.7 kpa 8 8 Sands Silty Sands Depth (ft) Depth (ft) 2 2 Sands before DDC after DDC before DDC after DDC Relative density, Dr (%) Dynamic shear modulus, G (Mpa) Constrained modulus, M (MPa) Figure 3.31 Comparison of relative density, dynamic shear modulus and constrained modulus before and after deep dynamic compaction (DDC) at station 143+5, Rt Station R Relative density, Dr (%) Dynamic shear modulus, G (MPa) Constrained modulus, M (MPa) Sands 2 1 ft =.348 m 1 tsf = 95.7 kpa Sand to Silty Sand Silty Sand to Sandy Silt Depth (ft) Sandy Silty to Clayey Silt Depth (ft) Sandy Silty to Clayey Silt Sand to Silty Sand 18 2 before DDC after DDC before DDC after DDC before DDC after DDC Relative density, Dr (%) Dynamic shear modulus, G (MPa) Constrained modulus, M (MPa) Figure 3.32 Comparison of relative density, dynamic shear modulus and constrained modulus before and after deep dynamic compaction (DDC) at station , Rt

45 153 Cone resistance, q t (MPa) φ (qt & s ' v) & F ' (sta.11+) (after Mitchell and Durgunoglu,1975) Initial After DDC 2 Vertical effective stress, s ' v (kpa) F ' = Vertical effective stress, s ' v (kpa) Cone resistance, q t (MPa) Figure 3.33 Relationship between 14 ' φ and q t at station Cone resistance, q t (MPa) φ (qt & s ' v) & F ' (sta.117+5) (after Mitchell and Durgunoglu,1975) Initial After DDC Vertical effective stress, s ' v (kpa) Vertical effective stress, s ' v (kpa) F ' = Cone resistance, q t (MPa) Figure 3.34 Relationship between 9 1 ' φ and q t at station 117+5

46 154 Cone resistance, q t (MPa) φ (qt & s ' v) & F ' (sta.141+) (after Mitchell and Durgunoglu,1975) Initial After DDC 2 Vertical effective stress, s ' v (kpa) F ' = Vertical effective stress, s ' v (kpa) Cone resistance, q t (MPa) Figure 3.35 Relationship between 14 ' φ and q t at station 141+ Cone resistance, q t (MPa) φ (q t & s ' v ) & F' (after Mitchell and Durgunoglu,1975) Initial After DDC F ' = Vertical effective stress, s ' v (kpa) Vertical effective stress, s ' v (kpa) Cone resistance, q t (MPa) ' Figure 3.36 Relationship between φ and q t at station 143+5

47 155 Cone resistance, q t (MPa) φ (q t & s ' v ) & F' (after Mitchell and Durgunoglu,1975) Initial After DDC 1 2 F ' =46 2 Vertical effective stress, s ' v (kpa) Vertical effective stress, s ' v (kpa) Cone resistance, q t (MPa) ' Figure 3.37 Relationship between φ and q t at station

48 156

49 157 CHAPTER 4 SHEET PILE INSTRUMENTATION DESIGN 4.1 OVERVIEW RT. 44 instrumentation project was initiated by the Massachusetts Highway Department Geotechnical Section in a detailed memo dated June 21, 21 (see Hourani, 21). This memo outlined the five sections chosen for instrumentation and depth and number of instruments to be monitored. Conceptual and detailed design of the instrumentation was prepared by Paikowsky et al. (21) outlining the pressure cell design, calibration methods and shop and field instrumentation installation details. The locations selected for the instrumentation are described in this chapter along with the type of instrumentation used for the monitoring. The instrumentation design, construction layout and the designation of the individual units are explained in detail. Further chapters provide details regarding the calibration of the individual vibrating wire total pressure cells (Chapter 5), thin film (tactile) sensors (chapter 6) and the installation of the instrumented sheet piles (Chapter 7). 4.2 LOCATION OF THE INSTRUMENTED SECTIONS The earth pressure monitoring concentrates on the stresses developing along the depth of the sheet pile wall and the wall s deformation in the deep peat deposits. Based on the boring logs, SPT and probing test results provided by the MHD (Massachusetts Highway Department) (refer to section 3.3), five sections were chosen by the MHD for instrumentation (Hourani, 21). These sections are: Station 11+(R), (R), 141+(R), 143+5(L), and (R). Using the cross sections presented in figures 3.2 to 3.6, it can be concluded that the deepest peat deposits coincide with the above five sections chosen for the instrumentation installation. Figure 3.7 presents a plan view of the instrumented sections along the road alignment and the location of relevant borings. Figure 4.1 presents the typical road cross-section in the instrumented locations. 4.3 INSTRUMENTATION REQUIREMENTS AND TYPE Instrumentation Requirements The following summary of requirements is based on Hourani (21) and was prepared by Paikowsky et al. (21). (a) Survey 1. Face of MSE wall at 5 feet intervals 2. Top of permanent sheeting walls at 5 feet intervals 3. Five roadway sections (L) 11+ (R) (R) 141+ (R) (R)

50 158 (b) Inclinometers Two inclinometers at each roadway section (c) Total Pressure Cells (TPC) Six (6) total pressure cells at each roadway section at distances 5 ft., 1 ft. and 15 ft. below access road at two locations (inside and outside) of the sheeting. (d) Monitoring Stages 1. Inclinometers and Pressure Cells At 1 construction phases ranging from (a) end of excavation to (j) full height of MSE wall construction. At each location no later than 48 hours after the construction stage or action has been completed. 2. Settlement points Once a week during all stages of sheeting and MSE wall construction. 3. Extension of Observation Period Based upon the performance of the wall readings may be required beyond the completion of the project General Layout Figure 4.1 describes a typical general cross-section of the instrumented locations including the MSE wall, sheet pile, inclinometers and pressure cells. Based on the soil conditions and the depth required for the instruments, anticipated pressures and ranges were calculated and chosen Selection of Instrumentation The most desirable feature to be considered in selecting instruments is reliability. Instruments should be the simplest to get the job done, be durable to withstand the ambient environment, and not be very sensitive to climatic and other extraneous conditions. Other factors to be considered are cost, skills required to process the data, interference to construction, instrument calibration, special access while monitoring, accuracy, and the range of predicted responses compared with the range of the instrument (Li, 1999). Based on the above criteria the following specifics were determined (Paikowsky et al., 21): 1. As long term monitoring under groundwater conditions is required, the use of vibrating wire equipment is recommended. 2. Rigid load cells are most appropriate to provide stiffness resembling that of the sheeting. 3. Typical total load cells are round and 9 inches in diameter (manufactured by Geokon, Slope Indicator, RocTest) these instruments can not be assembled on the sheeting used in the RT. 44 project without a modification that would alter the sheeting character. 4. A modified rectangular load cell mm (4 3 8 inch) manufactured by RocTest (type TPC) was chosen.

51 VIBRATING WIRE TOTAL PRESSURE CELLS General Earth pressure measuring devices fall into two categories. One is designed to measure the total stress at a point in an earth mass (Earth Pressure Cell EPC) and the other is designed to measure the total stress or contact stress against the face of a structural element (Total Pressure Cell TPC), see figure 4.2. Devices in the latter category are relatively accurate and reliable, provided the device is designed to behave similarly to the way the structure behaves. In addition, the earth pressures on a structure may be reasonably uniform for the structure as a whole, but are usually very not uniform over an area the size of a pressure cell. This condition results in a wide scatter of data that is difficult to interpret. Earth pressure measuring devices designed to measure stress at a point in a soil mass are not considered as accurate and as reliable as devices to measure stress against a structure. The main problem centers on the measuring device and the difference in the stiffness with the surrounding backfill Pressure Range Table 4.1 summarizes various approaches to the evaluation of the required pressure ranges estimated when choosing the instrumentation. The vibrating wire TPCs typically manufactured with the ability to withstand a pressure twice the maximum design pressure. The selected ranges are 15 psi (13 kpa) for the shallow load cells and 25 psi (172 kpa) for the deeper instruments TPC Specifications Figures 4.3 and 4.4 provide RocTest Inc. specifications of available EPC s and TPC s at the time of the instrumentation design. The TPC are hydraulic cells comprised of an oil filled pressure pad connected to a pressure transducer. The model TPC has a cross-sectional modulus rigidity of approximately psi ( kpa) making it suitable for embedment in concrete where temperature variations are small. The model TPC pressure cells are fitted with either a FPC pneumatic pad, a vibrating wire pressure transducers or an electrical 4 to 2 ma pressure transducers. The TPC model in rectangular shape is designed for the measurement of radial and tangential stresses. The high stiffness of the TPC pressure cells is due to the very narrow cavity with oil built in the cell and the high stiffness of the pad and the backplate. The vibrating wire transducer pressure cells are monitored manually or automatically using the MB-6T readout unit or the SENSLOG data acquisition system Instrumentation Modifications Figures 4.5 and 4.6 provide the RocTest construction details of the selected TPC in its standard manufacturing shape modified to the required thickness. In order to obtain maximum rigidity, load cell face flush with the wall and provide protection of the transducers

52 16 and wires, the following design modification were proposed specifically for RT.44 project (Paikowsky et al., 21). 1. Integrated backplate (3/16" thick), 8 inch 16 inch. 2. Recessed cell of.335 inch thickness to be flush with the sheeting when mounted through an opening in the sheet pile. 3. Cut an opening in the sheet pile approx. 4 1/8" 8 1/8" to mount the TPC with 1/16" gap around (isolate from axial stresses in the sheeting) to be filled with calking. 4. Reduced pressure range from the typical lowest range (25 psi). 5. Reconfigure the tubing from the sensor area to the transducer. 6. Attach a steel angle 4" 4" 1/4" to provide protection for cables and sensor. Tack welding most places with tapered shoe at the point below the lowest TPC. Figure 4.7 describes the details of the modified cells and figure 4.8 describes a photograph of the manufactured modified TPC Stiffness Evaluation Stress measurements in soils are difficult mostly due to the variation in the measurement conditions introduced by the measuring device. Variation in the stiffness between the zone of measurement to the surrounding areas may introduce increase or decrease in the stresses acting on that area depending if the deformation at the area decreases or increases, respectively. Similarity a protruding or recessed elements will result with similar effects. The modifications of the TPC and its adaptation to the sheet piles as described in the above section were accompanied by a detailed cell and cell/sheet pile stiffness evaluation carried out by Rowles and Paikowsky (22). This evaluation included hand calculation and finite element analysis and is described in Appendix D with the following major findings: 1. Based on idealized bending of a rectangular plate of constant thickness and simply supported edges, the maximum expected deflection of the pressure cell devices is.118 in at 25 psi. 2. The addition of the pressure cell and back angle at location A or B had very little effect on the stiffness of the typical sheet pile length that was examined. 3. The pressure cell alone was demonstrated to have a similar stiffness as that of the sheet pile system. Correspondingly, the addition of the pressure cells to the sheet pile walls will have negligible effects on local deformations. 4. The above analyses were based on simplifying assumptions that may differ substantially from the actual conditions in many cases. In general, the assumptions that were used probably resulted in larger deformations. The calculated deflections presented in Appendix D are therefore on the safe side compared to the actual deformation that may occur.

53 SINGLE CELL TACTILE PRESSURE SENSOR Tactile Sensor Technology Tactile sensor technology makes it possible to measure and present the normal stress distribution over an area in real time as demonstrated in figures 4.9 and 4.1. The figures present the normal stress distribution of a rubber bladder pushing sand against a mat sensor 5315#4 in a calibration chamber (described in chapter 6) before loading and after loading to a pressure of 3.5 psi. The 3-D views of the stress distribution are comprised of 216 sensing points made of 42 rows and 48 columns of intersection of sensing ink. The implementation of the tactile pressure sensor technology to geotechnical applications was first investigated and presented by Paikowsky and Hajduk (1997), with practical application of the technology to geotechnical related problems presented by Paikowsky and Palmer (1999), including modeling foundation and retaining wall experiments and Paikowsky and Rolwes (22) investigating the effects of grain size on interfacial and interparticle pressure measurements. The TekScan sensors are available in both grid-based and single load cell configurations. The grid based is also available in a wide range of shapes, sizes and spatial resolutions (sensor spacing). Their measuring pressures capabilities range from - to 6891 kpa ( to 1 psi). Each application requires an optimal match between the dimensional characteristics of the object(s) to be tested and the spatial resolution and pressure range provided by TekScan's sensor technology. The standard sensor consists of two thin, flexible polyester sheets that have electrically conductive electrodes deposited in varying pattern. In a simplified example as shown in figure 4.11, the inside surface of one sheet forms a row pattern while the inner surface of the other employs a column pattern. The spacing between the rows and columns varies according to the sensor application and can be as small as.5 mm. Before assembly, a patented, thin semi-conductive coating (ink) is applied as an intermediate layer between the electrical contacts (rows and columns). This ink, unique to TekScan sensors, provides the electrical resistance change at each of intersecting points. The electrical resistance decreases with the increased application force. When the two polyester sheets are placed on top of each other, a grid pattern is formed, creating a sensing location at each intersection. By measuring the changes in current flow at each intersection point, the applied force distribution pattern can be measured and displayed on the computer screen and the information can be graphically plotted as 2-D or 3- D displays as shown in figure 4.9 and 4.1. In use, the sensor is installed between two mating surface. The TekScan s matrixbased systems provide an array of force sensitive cells that enable you to measure the pressure distribution between the two surfaces. The 2-D and 3-D views show the location and magnitude of the force exerted on the surface of the sensors at each sensing locations. Force and pressure changes can be observed, measured, recorded, and analyzed throughout the test, providing a powerful engineering tool. There are two kinds of TekScan sensors available, complex sensor such as mat sensor 5315 as shown in figure 4.12, and a simple single load cell as shown in figure 4.13 The implementation of a multi sensor like the mat, requires expansive connections and although has great advantage (e.g. measuring stress distribution) its use encounters difficulties in harsh field environment. The importance of the actual stress distribution over a

54 162 sheet pile wall like RT. 44 is also secondary and hence the use of a single simple tactile cell was investigated Single Cell Construction The single cell provides measurement of pressure over a given area and a simple ohmeter can be used for data acquisition as described in chapter 6. The single cell shown in figure 4.13 is flexible, film thin element not suitable for direct field application, especially when considering the process of driving a sheet pile into the ground. A robust construction was therefore developed (Paikowsky, 22) allowing easy installation while providing protection to the sensing elements. The developed cell is comprised of a rectangular steel plate (8 inches (W) 2 inches (L)) on which two single cells are mounted as shown in figure With a diameter of 1.75 inches each, the center to center distance between the elements is 12 inches. The single elements are attached with non-shrinking glue to the steel plate as shown in figure 4.15(a) and protected against moisture by a rubber coating as shown in figure 4.15(b). A cut at the center of the plate provides passage of the two connectors through the back plate as shown schematically in figure 4.14 and photographed in figure The entire unit was capsulated in a thin metal cover and attached to the face of the sheet pile as shown in figure INCLINOMETER Inclinometers can be used to monitor horizontal movements within a soil mass or along a structure. Inclinometer consists of a casing installed in a vertical borehole or in a pipe installed within or attached to the surface of a structure. The inclinometer casing is grouted within the pipe. Normally, the lower end of the casing is anchored in rock and serves as a reference point. Pipe attached to a sheet pile is normally not anchored in rock and the top of the casing or the pipe are referenced to monuments outside the construction area. A probe, which measures the inclination of the casing at depths determined by the observer, is used for monitoring the full length of the casing. The probe is connected to a graduated electrical cable, which is used to lower and raise the sensor in the casing as depicted in figure The upper end of the cable is attached to a readout device that records the inclination of the casing from the vertical. Tilt readings and depth measurements are compared with initial data to determine movements that have occurred. Plastic, aluminum, and steel casing of various sizes and shapes have been successfully used with sheet pile cellular structures. Circular casing with guide grooves and square casing are available from US manufacturers. Casing connected to sheet pile sections must be attached so that casing remains undamaged and securely fastened to the sheet pile after the pile has been completely driven to the design depth. From that reason, a pipe attached to the sheet pile is used and the casing is grouted within the pipe following the installation. 4.7 PIEZOMETER The term piezometer is used to denote an instrument for monitoring pore pressures in a sealed-off zone of a borehole or fill. Piezometers can be classified into five types,

55 163 depending on the principle used to activate the device and transmit the data to the point of observation. The five types of piezometers include the open standpipe piezometer, the closed hydraulic piezometer, the diaphragm piezometer, the vibrating wire strain gage piezometer, and the semiconductor strain gage piezometer. An open standpipe piezometer has the advantage of simplicity and its use is widespread. These Piezometers were used in stations 11+ (R) and (R). Vibrating wire piezometers were used at the site at various sections and in particular along with the DDC at sections 11+ (R) and (R). Two vibrating wire piezometers had been installed at both sections on August 22, 23. Cone tip piezometers type 45 manufactured by Geokon were installed at the tip of standard 3/4 pipe and pushed into the peat as shown in figure SHEET PILE INSTRUMENTATION DESIGN Figure 4.2 presents a schematic of the instrumented sheet pile sections. The main instrumentation at each station consists of one inclinometer casing and two clusters of pressure cells. One cluster of pressure cell was designed to be installed in the inside web of the sheeting and the other on the outside web. As the sheeting profiles have male and female connections (depending on the station location), the instrumentations were designed for both options as presented in figure 4.2. The inclinometer casing is located in the corner of the sheet pile, made of a 4 diameter schedule 4 pipe secured by iron angles to the sheeting. Positions DEFJ are along the depth of the outside web of the sheet pile and positions AGBHC are along the inside web. The purpose of this arrangement of the pressure cells is to investigate the possible variation in the pressure measurements due to the location and the way it is being affected by arching or other preferable stress transformation. The top of the instrumented sheet pile was designed to be two feet above the ground surface. At each instrumented station, three pairs of vibrating wire total pressure cells (TPC) were designed to be instrumented at a distance of 7 feet, 12 feet, and 17 feet from the top of the sheet pile, equivalent to 5 feet, 1 feet and 15 feet depth from the ground surface. A two unit single tactile cells were designed to be instrumented at position G, 9.5 feet from the top of sheet pile (7.5 feet depth from the ground surface). Additional two tactile sensors units were designed to be instrumented at positions J and H, both 14.5 feet from the top of the sheet pile, 12.5 feet depth from the ground surface as shown in figures 4.2 and The distance between two adjacent TPCs along the depth is 5 feet. The distance between the TPC and the adjacent tactile sensors is 2.5 feet. The distance between two adjacent tactile sensors is 5 feet. As a preparation for the installation, six cut-outs are performed at positions A, B, C, D, E, and F, which are oversized compared to the pressure pads of the VWTPC. The oversized cut comes to eliminate stress transformation from the sheeting into the pressure cell hence ensuring no contact between the cell pressure pad (see figures 4.7, 4.8) and the sheeting while being flush with the sheeting surface. The tactile sensors were attached on the sheeting surface hence only a 3/4 opening was required to transfer the connectors and allow the electrical cables to be led through the protected chase created by a /4 steel angle as detailed in figures 4.22 and The tactile sensors mounting on the sheeting is described in figure 4.24 and the photograph in figure 4.17 showed both cells when installed in the sheet pile (additional photographs are presented in chapter 7).

56 SECTIONS LAYOUT AND INSTRUMENTATION DESIGNATION Instrumented Section The instrumentation used at each station are summarized in table 4.2 and described below. (a) Station 11+ (R) At station 11+ (R), a total of six TPCs along with six single cell (3 units) tactile sensors and one inclinometer casing were installed. A piezometer was installed temporarily to monitor the change in the pore pressure during the deep dynamic compaction (DDC). (b) Station (R) There are a total of six TPCs along with six single cell (3 units) tactile sensors and one inclinometer casing were installed at station (R). A piezometer was installed temporarily to monitor the change in the pore pressure during the deep dynamic compaction (DDC). (c) Station 141+ (R) At station 141+ (R), a total of six TPCs along with six single cell (3 units) tactile sensors and one inclinometer casing were installed for instrumentation. (d) Station (L) There are a total of six TPCs and one inclinometer casing were installed for instrumentation. No single cell tactile sensor was installed for instrumentation at this station. (e) Station (R) At this station, a total of six TPCs along with six single cell (3 units) tactile sensors and one inclinometer casing were installed Instrumentation Designation and Location Table 4.3 presents the serial numbers of the instrumented pressure cells at the five stations. The relevant locations are identified in figure 4.2. Table 4.4 provides the numbering of each instrument and its position along with the pressure cells serial number, calibration range, cable length, instrumented station, and test meter. As shown in figure 4.2, positions A and D are located at 7 feet from the top of the instrumented sheet pile. Positions B and E are at 12 feet from the top of the instrumented sheet pile and positions C and F are at 17 feet from the top of the instrumented sheet pile. 4.1 SUMMARY Based on the geologic conditions, instruments reliability, cost and sensitive to the extraneous condition and so on, five stations (stations 11+ R, R, 141+ R, L, and R) located in the cranberry bogs with deep peat deposits finally were determined to be instrumented with inclinometers and modified vibrating wire total pressure cells (VW TPC) along with single tactile sensors to monitor the sheet pile and soil body deformation and the total lateral earth pressure developing in the peat respectively during the entire construction period. At each selected station, it was designed to be instrumented with two clusters of total pressure cells along with two inclinometer casings. One cluster of pressure cells ( three VW

57 TPCs along with 4 single tactile sensors) were designed to be instrumented at positions AGBHC on the inside web sheeting and the other cluster of pressure cells (three VW TPCs along with two single tactile sensors) were to be instrumented at positions DEJF on the outside web sheeting (refer to figure 4.2). The top of the instrumented sheet pile was designed to be 2 ft above the ground surface. The VW TPCs were designed to be 5ft, 1ft, 15ft respectively below the ground surface and single tactile sensors were to be 7.5ft and 12.5ft below the ground surface. At each selected station, one inclinometer casing was designed to be attached on the sheeting to monitor the sheet pile deformation and the other one was designed to be installed in the backfill side (15 ft from the embankment) to monitor the soil body deformation induced by the latter embankment construction. Piezometer and standing pipe piezometer were also chosen to monitor the water table level changes. 165

58 166 Table 4.1 Evaluation of the pressure range for the TPC (Paikowsky et al., 21) Cell # Depth from top of peat (ft) Calc. passive stress (ksf) (initial GTR report) Hydrostatic pressure (ksf) including increased water elevation for barges Subtotal of 2 and 3 (ksf) Re-evaluation of pressure cell stress based on φ=25 (ksf) Re-evaluation of pressure cell stress based on c=25 psf (ksf) Subtotal of 5 and 3 (ksf) Design range for cells Max. calc. (psi) (rounded) Cell range to be used (psi) Note: 1 ksf = 6.94 psi Table 4.2 Summary of the instruments used at the five monitored stations Station VW TPC (#) Tactile (#) Inclinometer (#) Piezometer Standing Pipe Piezometer Sta.11+(R) Yes (temporary) Yes Sta.117+5(R) Yes (temporary) Yes Sta.141+(R) Yes Sta.143+5(L) Yes Sta (R)

59 167 Table 4.3 Summary of pressure cells numbering and designation at the five monitored stations Vibrating Wire Pressure Cell (TPC) # TekScan Tactile Sensor # Station Location Location A B C D E F G H J 11+ R #237 #238 #2388 #2367 #2381 #2393 8up/9down 6up/5down 4up/3down R #2366 #2382 #2389 #2368 #2384 #2386 1up/2down 1up/11down 14up/15down 141+ R #2373 #2379 #2387 #2374 #2378 #239 19up/2down 21up/22down 23up/24down L #2369 #2376 #2391 #2371 #2377 #2392 N/A N/A N/A R #2365 #2375 #2385 #2372 #2383 # up/17down 12up/13down 17up/18down

60 Table 4.4 Instrumentation layout and designation at the five stations VIBRATING WIRE TOTAL PRESSURE CELL TEKSCAN TACTILE SENSOR TPC Calibration Cable Section Location Test Tekscan Calibration Section Location S/N Range Length Section Cell meter Sensor Range Section Cell Comments 78E# psi ft # position (in Lab) S/N psi # position A GK G UP rubber coating only A RocTest G DOWN rubber coating only D RocTest J DOWN rubber coating only D RocTest J UP rubber coating only A GK H DOWN rubber+complete Alum A RocTest H UP rubber+complete Alum D GK G UP rubber+alum epoxy D RocTest G DOWN rubber+alum epoxy A RocTest H UP rubber coating+alum limited area D RocTest H DOWN rubber coating+alum limited area B GK J UP rubber coating+alum limited area B GK J DOWN rubber coating+alum limited area E GK G UP rubber coating+alum limited area E GK G DOWN rubber coating+alum limited area B GK H UP rubber coating+alum limited area B GK H DOWN rubber coating+alum limited area E GK J UP rubber coating+alum limited area B GK J DOWN rubber coating+alum limited area E RocTest UP rubber coating+alum limited area E GK DOWN rubber coating+alum limited area C RocTest UP rubber coating+alum limited area F RocTest DOWN rubber coating+alum limited area C RocTest UP rubber coating+alum limited area C RocTest DOWN rubber coating+alum limited area C RocTest F RocTest C GK F GK F RocTest F RocTest 168

61 Figure 4.1 Typical road cross-section in the instrumented locations (Paikowsky et al., 21) 169

62 mm Electrical Cable 11.6 mm Vibrating Wire Pressure Trnasducer Pressure Cell Pad Model TPC Pressure Tubing Pressure Gage Model EPC 23.2 mm mm Pressure Transducer Housing 6.35 mm Pressure Cell Pad Model TPC &27.94 mm Schematic Diagram of Model TPC and EPC Pressure Pad Pressure Figure 4.2 Schematic of Model TPC and EPC

63 Figure 4.3 General information of RocTest TPC 171

64 Figure 4.4 Specifications of RocTest TPC s and EPC s 172

65 Figure 4.5 Details of the selected TPC modified to a thickness of.38" (RocTest-first round design) 173

66 Figure 4.6 Cross section of TPC and capsulated oil film (RocTest) 174

67 175 9" 9" Transducer Steel Plate 8" Pressure Cell Sheet Pile 16" 4" 8" FRONT VIEW BACK VIEW (3/16)" Back Plate.335" Sheet Pile Pressure Pad Cross-Section View of Pressure Cell and Sheet Pile Figure 4.7 Detailed modifications of the pressure cell and the back plate layout

68 176 (a) front view of TPC (b) back view of TPC Figure 4.8 The configuration view of TPC cell

69 kpa Figure D view of stress distribution over a mat tactile sensor 5315#4 (manufactured by Tekscan) before loading 3 kpa Figure D view of stress distribution over the contact area of the mat tactile sensor 5315#4 (manufactured by Tekscan) after loading to 24 kpa

70 178 Figure 4.11 The exploded view of TekScan configuration (website of Tekscan, Inc.) Figure 4.12 The plane view of mat sensor #5315 (website of Tekscan, Inc.)

71 179 Figure 4.13 Photograph of a single cell tactile pressure sensor STEEL PLATE 2in A STEEL PLATE 2in A.2in.9in SLOT* SECTION A-A * Note : Beveled edges on one side of slot 12in TACTILE SENSOR DIAMETER OF 2in CONNECTION 13.5in FRONT VIEW PLATE WITH TEKSCAN CELLS PROJECT: 1.15 GEOSCIENCES TESTING AND RESEARCH, INC. ROUTE 44 INSTRUMENTATION - SHEETING DESIGN DRAWN BY: JCA BACK VIEW PLATE WITH TEKSCAN CELLS MOUNTED TEKSCAN/GTR PRESSURE CELL SCALE: N/A SHEET: 8 of 8 DATE: 11/1/2 Figure 4.14 The construction of the single cell tactile pressure sensor (Paikowsky et al., 22)

72 18 Figure 4.15 Photograph of single cells (a) attached on the steel plate and (b) coated with protective rubber Figure 4.16 Photograph of the back view of the single cell tactile pressure sensor

73 Figure 4.17 Photograph of the complete single cell tactile pressure sensor 181

74 182 Read cable marks at top of casing Stickup Depth to Shallowest reading as per cable marks Ground Surface or other suitable reference elevation Inclinometer Probe Detail 1 A+ B- B A- Detail 1 Note: Inclinometer probe is about 8 mm long and about 25 mm in diameter Figure 4.18 Schematic of Inclinometer Probe Piezometer Cable Ground Surface Water Level Portable Readbox Hollow Steel Pipe Expected Change in Level Piezometer Filter Stone Figure 4.19 Schematic of Piezometer

75 183 9'' 19.5'' 9'' 9'' 19.5'' 9'' 2'' 112 Flange 7'' 3'' Outside Web Sta.11+(R) Sta.141+(R) 13.4" 13.4" 3'' 3'' Inside Web Inside Web 7'' 3'' Outside Web Sta (L) Sta (R) Sta (R) Flange 112 2'' Inclinometer Casing 2 FEET 4 inches D (TPC) 5 FEET A (TPC) Vibrating Wire Total Pressure Cell (TPC) (TPC) A (TPC) D 8 inches 2.5 FEET G (Tekscan) 5 FEET (Tekscan) G E (TPC) B (TPC) (TPC) B (TPC) E J (Tekscan) optional.75inch diameter opening Tactile Cell TYP. H (Tekscan) 5 FEET (Tekscan) H (Tekscan) J F (TPC) C (TPC) (TPC) C (TPC) F Figure 4.2 Schematic of the sheet pile instrumentation layout

76 184 2ft Sheet Pile 5ft Cut-out for TPC Typ. 1ft 2.5ft Optional.75 inch diameter opening 15ft 4in 2.5ft 8in 2in GEOSCIENCES TESTING AND RESEARCH, INC. ROUTE 44 INSTRUMENTATION - SHEETING DESIGN PROJECT: 1.15 SHEETING PREPARATION LAYOUT DRAWN BY: SCALE: SHEET: DATE: JCA N/A 2 of 8 1/18/2 Figure 4.21 Schematic of sheet pile presentation for instrumentation (Paikowsky et al., 22)

77 185 Back Plate 2ft 1/4" 4" 4" x 4" x 1/4" Angle Transducer Cell Cables 5ft Sheet Pile 1/4" 4" 1ft 1/4" DETAIL 1: PRESSURE CELL AND BACK PLATE - PLAN VIEW NOTE: Weld 4" every 1 foot along sheet 15ft DETAIL 1 4" x 4" x 1/4" Angle Notched to fit over Back Plate Back Plate Back Plate Cell Optional Tekscan 8x2x.1 inch TLC Welded Cover DETAIL 2: ANGLE PROTECTION END - FRONT VIEW GENERAL WELD NOTES: 1. ALL WELDED CONNECTIONS SHALL BE WELDEDTO CONFORM TO SPECIFICATION A-233, E-7 SERIES. DETAIL 2 2. ALL WELDING SHALL CONFORM TO THE LATEST EDITION OR ANSI/A WS D1.1. GEOSCIENCES TESTING AND RESEARCH, INC. 1ft ROUTE 44 INSTRUMENTATION - SHEETING DESIGN DETAILS FOR INSTRUMENTATION ANGLE PROTECTION PROJECT: 1.15 DRAWN BY: JCA SCALE: N/A SHEET: 4 of 8 DATE: 1/18/2 Figure 4.22 Details of instrumentation angle protection (Paikowsky et al., 22)

78 186 Transducer 2ft Cell Cables Back Plate 5ft 4" x 4" x 1/4" Angle 1ft DETAIL 3 DETAIL 3: SIDE VIEW ANGLE PROTECTION NOTE: See Sheet 3 of 4 for Welding Details 15ft Cell Sheet Pile Back Plate 4" x 4" x 1/4" Angle Notched to fit over Back Plate Welded Cover DETAIL 4: ANGLE PROTECTION END - SIDE VIEW 1ft DETAIL 4 GEOSCIENCES TESTING AND RESEARCH, INC. NOTCHED ANGLE BEFORE WELDING ROUTE 44 INSTRUMENTATION - SHEETING DESIGN DETAILS FOR INSTRUMENTATION ANGLE PROTECTION PROJECT: 1.15 DRAWN BY: JCA SCALE: N/A SHEET: 5 of 8 DATE: 1/18/2 Figure 4.23 Details of instrumentation angle protection (Paikowsky et al., 22)

79 187 SHEET PILE STEEL PLATE PRESSURE CELL 2in 13.5in.2in 8in 9in FRONT VIEW BACK VIEW PROJECT: 1.15 GEOSCIENCES TESTING AND RESEARCH, INC. ROUTE 44 INSTRUMENTATION - SHEETING DESIGN TEKSCAN/GTR PRESSURE CELL AND BACK PLATE LAYOUT DRAWN BY: JCA SCALE: N/A SHEET: 7 of 8 DATE: 11/1/2 Figure 4.24 Details of tactile cell mounting over the sheet pile (Paikowsky et al., 22)

80 188

81 189 CHAPTER 5 CALIBRATION OF THE VIBRATING WIRE TOTAL PRESSURE CELLS (TPC) 5.1 GENERAL The vibrating wire total pressure cells (VW TPC) and earth pressure cells (EPC) are designed to measure the total stress acting on and in bulk materials. For example, in embankments, mine backfill and mass concrete, or used in measuring the contact pressures on the tunnel linings, foundations, slurry and retaining walls, culverts or other embedded structures. Chapter 4 describes the cells construction and design as part of the sheet pile instrumentation. In all, 3 TPC cells had been calibrated at the geotechnical engineering research laboratory of the University of Massachusetts Lowell for the instrumentation of the sheet pile installed in the peat and monitored in this project. The following sections describe the calibration of the cells prior to their installation in the sheet piles. 5.2 THE TPC CALIBRATION SYSTEM The schematic of the calibration system for the TPC is presented in figure 5.1 and is made up of four major components: (1) Pressure control system (2) Temperature controlled chamber Pressure chamber (3) Readout system. FlexPanel manufactured by Humboltd Mfg. Co. shown in figure 5.2, was used as a pressure control system. The panel is used to control and monitor flow of liquids in and out of various testing apparatuses. This equipment is designed to work with a maximum air pressure of 15 psi. By applying air pressure on water in a burette, the water pressure can be applied via a bladder in a pressure chamber to the TPC. The temperature controlled chamber presented in figure 5.3 was constructed of an insulated sealed small structure (L8ft H6ft W4ft) with one air conditioner for temperature reduction. A bypass of the air conditioner control system allowed its continuous operation and the maintenance of a constant temperature as desired. The small structure housed the pressure chamber system, allowing the TPC calibration for different temperatures. Figure 5.4 presents a cross-sectional view of the pressure chamber used for testing the TPC in peat. This system was initially developed in the Geotechnical Eng. Research Laboratory at UML for testing mat tactile sensors and is described by Palmer (1999). The system includes a water filled rubber bladder in the lower chamber as shown in figure 5.5. The bladder is connected to the pressure control system by a ¼ hose at its bottom, by which the pressure is controlled. A pressure transducer is connected at the bladder connection for direct measurement of the applied pressure. The bladder is then covered with a layer of peat on which the transducers rest. A rigid cover is then applying as a reaction and the view of the closed system is shown in figure 5.6. Upon application of pressure to the bladder, the bladder transmits the pressure via the peat to the pressure pads of the TPC. Figure 5.7 presents a photograph of the read-out systems. A vibrating wire readout box GK-43 designed to be used with all of Geokon s vibrating wire sensors was used for reading the TPC output. The GK-43 allows to read and display readings including

82 19 temperature, and store all the data in the memory that later can be transmitted to a host computer. The readout system also includes the voltmeter (manufactured by Hewlett Packard) with the accuracy of.1 mv used for the pressure transducer as shown in figure CALIBRATION PROCEDURE The calibration procedure included the following steps: Step 1: Calibration of the pressure transducer (performed one time before the tests) and establishing a calibration factor. The calibration was performed using a special pressure device. See Appendix E for results. Step2: Connect all the elements together as shown in figure 5.1. Step 3: Cover the surface of the bladder with a plastic sheet and fill the gap above the bladder with peat layer about.5 inch thick as shown in figure 5.8. Step 4: Obtain the pressure cells initial readings before their installation in the calibration chamber. Step 5: Place two TPC attached by the notched wood cover such that the pad is in the peat. The TPC and the wood are installed in the chamber as shown in figure 5.9. Step 6: Install the stiff metal cover over the pressure chamber and tighten the bolts as shown in figures 5.4 and 5.6. Step 7: Connect the cables from the pressure cells to the vibrating wire instrumentation readout box. Step 8: Close the door of the temperature chamber and operate the air conditioner (if needed) to reduce the temperature to the one required for the testing and achieve stabilized temperature. The TPC were calibrated in temperatures of 4, 6, and 8 F. Step 9: Apply pressure via the pressure control system and record the readings of the pressure cells using the readout box while continue to record the applied pressure via readings of the pressure transducer using a voltmeter. Step 1: Increase gradually the pressure usually by steps of 1 psi to the required peak pressure of 15 or 35 psi (see table 4.3), and then unload the pressure in steps and record the readings. Step 11: Record final readings when the pressure decreases back to zero and the readings stabilized. Step 12: Close the pressure control system, disconnect the cables and pressure transmission hose, disassemble the pressure chamber and extract the TPC. Step 13: Analyze the readings to obtain the calibration factors. It should be noted that the pressure values appeared on the pressure control system are not the correct pressures acting on the pressure cells. The pressure acting on the TPC cells should be equal to the readings measured by the transducer, which is equal to the pressure appearing on the pressure control system plus the water pressure in the burette. The transducer pressure values were therefore used in the calibration process.

83 CALIBRATION FACTORS Overview During the calibration process, each TPC was loaded and unloaded (to 15 or 35 psi) at 4 F, 6 F, and 8 F. The relationship between the gage readings and the applied pressure acting on them at different temperatures was drawn and analyzed. The results show that the gages respond linearly with the pressure both in loading and unloading. The obtained relations for the different TPC calibrations under constant pressure or temperature were plotted and are presented in appendix E. Overall, the temperature effect on the TPC readings under the constant pressure are minimal. The following section presents in detail the calibrated results for one TPC with a summary presenting the calibration factors for all the TPC provided in tables 5.1 to Presentation of the Calibration Factors Figure 5.1, 5.11 and 5.12 present the calibration results for TPC cell 78E2371 at temperatures 4 F, 6 F, and 8 F, respectively. It can be observed that the gage readings at the different temperatures decrease linearly with the increasing of the pressure. The temperature has a small influence on the calibration factors. The following equation is used in the interpretation of the vibrating wire total pressure cells: P = CF (L 1 -L ) (8.1) Where: P = calculated pressure, in psi CF = calibration factor, in psi/lu L, L 1 = initial and current reading, in LU Figures 5.13 to 5.15 present the calibration error for TPC cell 78E2371 at temperatures 4 F, 6 F, and 8 F, respectively. The error estimation was calculated by taking the difference between the actual pressure (for the given temperature) and that calibrated pressure using the manufacturer s calibration factors (from the factory) determined at 7 F (see table 5.1 to 5.3 and Appendix E). This error calculation is expressed as: Error (%) = (P 1 P )*1 / P 1 (8.2) Where: P 1 = actual Pressure, in psi P = calculated Pressure, in psi This error calculation does not use the developed calibration factor, hence guarantees the maximum possible error with consideration of temperature. Error calculations and graphs for all 3 TPC s are presented in Appendix E. Based on the error calculations it can be concluded that using the manufacturer s calibration would result with an error that does not exceed 5% during either loading or unloading. Figures 5.16 to 5.18 present the percent error of the readings when using the calibration factors provided by the factory against the applied pressure. The error estimation was calculated by taking the difference between the TPC reading under a certain pressure (for the given temperature) and that measured during the factory calibration under the same

84 192 pressure in 7 F. This error calculation guarantees the maximum possible error without consideration of temperature calibration which was used for in developing figures 5.13 to 5.15 and was also used in the interpretation of the actual field measurements. It can be observed that although greater than before, under a wide range of temperatures, the percent error does not exceed ±5% during either loading or unloading. Figure 5.19 presents the affect of temperature on the gage readings for TPC 78E2371. It can be noticed that under the constant loading, the gage readings of the cell changed very little with the changes of temperatures, which supports the aforementioned conclusion that the effect of the calibrated temperature in the examined range is limited and even without its consideration the practical significance for the field measurements is limited Summary of Results Calibration factors were developed based on the data analysis of the relations between the applied pressure and gage readings under three temperatures for all 3 vibrating wire total pressure cells (TPC). For all TPCs, the gage readings decreased linearly with the increasing in the applied pressure. The temperature effects are limited and the gage readings linearly change with the temperature. The use of the factory calibration factors results with maximum expected errors, commonly less than 5% for all the 3 cells, under different temperatures. Table 4.3 presents the serial numbers for all the VW TPC including their cable length, allowable applied pressure range, and readout instrument. All the readings obtained by using GEOKON readout box GK-43, should be multiplied by 1.156, when compared to the readings obtained using the RocTest box. All the calibration factors for the TPC cells derived from the RocTest readings including those calibrated in the factory. Tables 5.1 to 5.3 present the calibration factors for all the 3 TPC at different temperatures. Appendix E provides all the calibration data, graph and error assessment for all the cells. Based on the measured temperature effects on the TPC, it can be assumed that the calibration factors of the TPC are linearly changing with the temperature. If gage readings of the TPC cells are taken at one temperature, the actual pressure acting on the pressure pad at another temperature can be calculated using interpolated calibration factors for that temperature. The interpretation of the field readings used this observation and applied interpolated calibration factors based on the TPC temperature reading in the field and the calibration factors for the various temperatures presented in tables 5.1 to 5.3. Procedure is described in Chapter 8.

85 193 Table 5.1 Reported and measured TPC calibration factors Series Number (TPC) 78E 2365 (psi/lu) 78E 2366 (psi/lu) 78E 2367 (psi/lu) 78E 2368 (psi/lu) 78E 2369 (psi/lu) 78E 237 (psi/lu) 78E 2371 (psi/lu) 78E 2372 (psi/lu) 78E 2373 (psi/lu) 78E 2374 (psi/lu) Factory F F F Table 5.2 Reported and measured TPC calibration factors Series Number (TPC) 78E 2375 (psi/lu) 78E 2376 (psi/lu) 78E 2377 (psi/lu) 78E 2378 (psi/lu) 78E 2379 (psi/lu) 78E 238 (psi/lu) 78E 2381 (psi/lu) 78E 2382 (psi/lu) 78E 2383 (psi/lu) 78E 2384 (psi/lu) Factory F F F Table 5.3 Reported and measured TPC calibration factors Series Number (TPC) 78E 2385 (psi/lu) 78E 2386 (psi/lu) 78E 2387 (psi/lu) 78E 2388 (psi/lu) 78E 2389 (psi/lu) 78E 239 (psi/lu) 78E 2391 (psi/lu) 78E 2392 (psi/lu) 78E 2393 (psi/lu) 78E 2394 (psi/lu) Factory F F F

86 194 Temperature Control System Pressure Chamber Switch Vibrating Wire Readout Steel Cover Wood Cover Air Pressure Supply Peat TPC Bladder Voltage Readout Pressure Transducer Water Supply Pressure Control System Deairing System Figure 5.1 Schematic of the calibration system Figure 5.2 Photograph of the FlexPanel used as pressure control system (manufactured by Humboltd Mfg. Co.)

87 195 Figure 5.3 Photograph of the temperature controlled structure nut washer fillet welds 19.5 mm (3/4") threaded rod 12 mm x 51 mm (4" x 2") aluminum channel 6.4 mm (.25") thick plate masking tape 25.4 nn (1") sq. x 3.2 mm (.125") w.t. Al. tubing 6.4 mm (.25") thick plate 6.4 mm (1/4-2) bolt 15.9 mm typ. Peat Pressure bladder TPC Wood Cover 15.9 mm (.625 in.) material retention frame 6.4 mm (.25") thick bottom reation plate 38.1 mm (1.5") thick wood table To electro-pneumatic transducer Steel I-shape supports located below table surface Figure 5.4 Cross-section of the adopted for the TPC pressure chamber system (modified from Palmer, 1999)

88 196 Figure 5.5 Photograph of the pressure bladder in the chamber Figure 5.6 Photograph of the pressure chamber with the pressure cells

89 197 Figure 5.7 Photograph of the readout system for the vibrating wire TPC and the voltmeter of the pressure transducer attached to the bladder Figure 5.8 Photograph of the peat overlaying the bladder in the chamber

90 198 Figure 5.9 Photograph of the TPC embedded in the peat and covered by a wood to accommodate the pressure tubes 78E2371 at 4F Loading: P(psi) = *(Li-Lo) R 2 = Unloading: P(psi) = *(Li-Lo) R 2 = Combined: P(psi) = *(Li-Lo) R 2 = loading unloading Combined Linear (loading) Linear (unloading) Linear (Combined) Li-Lo (LU) Applied Pressure (psi) Figure 5.1 Gage readings vs. applied pressure for TPC 78E2371 at 4 F